The  RALPH  D.  REED  LIBRARY 

o 

DEPARTMENT  OF  GEOLOGY 
UNIVERSITY  OF  CALIFORNIA 

LOS  ANGELES,  CALIF. 


.  >^fc 

LIBHABY 


FIRST  BOOK  IN  GEOLOGY 


DESIGNED  FOR 


THE    USE    OF   BEGINNERS 


BY 


N.  S.  SHALER,  S.D., 

PROFESSOR  OF  PALEONTOLOGY  IN  HARVARD  UNIVERSITY 


D.    C.    HEATH   &   CO.,    PUBLISHERS 

BOSTON        NEW  YORK        CHICAGO 


w  -> 

O  &  '  -  525  i,larf«6t  St   \ 

v       Garfield  13        'Jf 

.  • 


Entered,  according  to  Act  of  Congress,  in  the  year  1884,  by 

N.  S.  8HALER, 
In  the  Office  of  the  Librarian  of  Congress  at  Washington. 


PRINTED  IN   U.  S.  A. 


INTRODUCTION. 


First  Book  of  Geology  is  intended  to  give  the 
beginner  in  the  study  of  that  science  some  general 
ideas  concerning  the  action  of  those  forces  that  have 
shaped  the  earth.  Only  a  very  small  part  of  the  more 
important  facts  that  constitute  the  store  of  the  geologist 
is  given  within  its  pages.  The  effort  of  the  writer  has 
been  to  select  from  that  ample  store  such  topics  as  will 
give  the  student  an  idea  of  the  world  as  a  great  workshop, 

\  where  the  geological  forces  are  constantly  working  towards 
definite  ends. 

The  greatest  and  most  easily  seen  of  these  agents  is 
water,  therefore  the  book  begins  with  a  study  of  water  in 

v  its  most  simple  mode  of  action.  Next,  the  action  of  heat, 
in  its  various  ways  of  working,  should  command  the  stu- 
dent's attention.  Finally,  the  animal  and  vegetable  life 
of  the  earth,  whose  forces  come  mainly  from  the  action 
of  heat,  receive  some  attention. 

It  will  be  well  for  the  student  to  have  a  general  idea  of 
the  solar  system,  for  all  this  machinery  of  the  earth's 
workshop  depends  in  a  large  measure  on  the  way  in  which 


IV  INTRODUCTION. 

the  sun  acts  on  the  earth.  The  sun  is  related  to  the 
earth  as  the  boiler  to  the  steam  engine,  and  it  is  well 
to  know  something  of  its  nature,  and  of  the  motions  of 
the  earth  about  it,  before  looking  at  its  effects.  Although 
this  preliminary  knowledge  is  desirable,  it  is  not  indispen- 
sable, for  the  text  explains  itself. 

However  carefully  a  text-book  may  be  prepared,  and 
however  well  it  may  be  used,  it  cannot  of  itself  alone  give 
much  insight  into  nature.  This  must  come  from  the  use 
of  the  student's  eyes  and  mind.  The  most  the  student 
can  expect  from  the  book  is  an  idea  of  what  is  to  be  seen 
in  the  outer  world.  He  will  not  really  know  much  of  this 
world  until  he  has  learned  to  read  the  facts  himself.  The 
real  use  of  the  book  to  the  beginner  is  to  show  those 
things  that  cannot  be  readily  seen,  and  to  set  forth  the 
nature  of  the  forces  that  act  in  propelling  the  earth's 
machinery. 

It  will  be  noticed  that  some  of  the  most  important 
points  in  the  mechanism  of  the  earth  are  repeatedly  re 
ferred  to  in  successive  chapters.  This  has  been  done  with 
a  view  to  fixing  the  memory  of  the  most  important  truths 
by  looking  at  them  from  many  sides.  Every  one  who  has 
taught  geology  must  have  seen  the  importance  of  con- 
sidering each  important  fact  from  many  points  of  view. 

In  using  this  book,  the  student  should,  under  each  chap- 


INTRODUCTION.  V 

ter,  seek  to  find  if  there  are  not  some  facts  in  his  neigh- 
borhood that  have  a  bearing  on  the  matter  given  in  the 
text.  Some  of  the  chapters  give  an  account  of  matters 
which  are  found  only  in  a  few  parts  of  the  earth.  Rarely 
will  a  student  find  himself  in  a  position  to  see  with  his 
own  eyes  the  structure  or  action  of  volcanoes,  or  the  way 
in  which  caverns  are  formed,  but  there  will  always  be 
some  part  of  the  book  where  he  can  help  his  understand- 
ing of  the  matter  with  his  own  eyes. 

Let  me  also  urge  upon  the  students  who  use  this  little 
first  book  that  they  help  themselves  to  a  more  pleasant 
relation  with  their  world  by  making  collections  of  min- 
erals, fossils,  plants,  and  other  objects  that  will  tell  them 
something  of  nature.  Not  only  is  there  to  most  young 
people  a  peculiar  charm  in  owning  a  collection  of  this 
sort,  but,  if  the  owner  will  learn  all  he  can  about  each 
object  in  his  collection,  he  will  soon  come  to  have  a  valu- 
able fund  of  precise  and  well-remembered  information  that 
will  stay  by  him  all  his  life ;  while  the  things  that  have 
had  nothing  but  words  to  fix  them  on  the  memory  will 
soon  fade  away. 

But,  above  all,  I  beg  each  reader  and  student  of  this 
book  to  remember  that  this  earth  is  full  of  lessons  that 
can  be  read  by  every  one  who  wishes  to  know  them,  — 
lessons  that  will  widen  the  mind  and  make  the  soul  more 


VI  INTBODUCTION. 

fit  for  the  duties  and  pleasures  of  life.  The  inattentive 
eye  never  gets  this  teaching;  but,  to  those  who  learn  to 
look  rightly  on  this  world,  it  gives  without  stint  from  its 
great  store  of  truth. 

The  woodcuts  in  this  book  were  drawn  on  wood  by 
Mr.  Charles  E.  Robinson.  They  are  mostly  original,  but 
I  am  indebted  to  the  works  of  Professor  J.  D.  Dana, 
Joseph  Leidy,  and  H.  A.  Nicholson,  and  to  the  Seaside 
Studies  in  Natural  History  of  Mrs.  E.  C.  Agassiz,  and 

Alexander  Agassiz,  for  certain  figures. 

N.  S.  SHALER. 

CAMBRIDGE,  MASS.,  Jan.  1. 1884. 


QUESTIONS  FOR  THE  USE  OF  STUDENTS. 


IT  should  be  noticed  that  sometimes  these  questions  are 
designed  to  direct  the  student  to  his  personal  experiences 
as  well  as  to  the  statements  of  the  book.  A  few  questions 
are  enclosed  in  brackets.  These  may  be  omitted,  as  they 
are  a  little  outside  of  the  text. 

CHAPTER  I. 

Lesson  I.    Page  1. 

1.  What  variety  do  we  notice  in  river  pebbles?  2.  What  is  the 
history  of  these  river  pebbles?  3.  In  what  way  do  they  journey  down 
stream?  4.  Compare  the  making  of  boys'  marbles  with  the  making 
of  pebbles.  5.  How  does  frost  help  in  the  work?  6.  How  can  this 
be  shown  by  means  of  a  bomb  shell  ? 

Lesson  II.    Page  5. 

1.  What  is  a  beach?  2.  How  does  the  sea-beach  wear  its  pebbles? 
3.  What  is  formed  of  the  ground-up  pebbles  ?  4.  Is  the  same  grinding 
up  carried  on  in  a  river?  5.  How  do  the  two  processes  differ? 
6.  Whereabouts  on  the  beach  are  the  pebbles  the  largest  ?  7.  How 
does  the  sea  begin  the  process  of  pebble  making  ? 

Lesson  III.    Page  8. 

1.  What  is  a  glacier?  2.  How  do  its  pebbles  differ  from  those 
made  in  rivers  and  on  beaches?  3.  What  are  moraines?  4.  How  are 
glacial  pebbles  made?  5.  Finding  these  pebbles  where  no  glaciers 
now  exist,  what  do  they  teach  us?  6.  Where  are  glacial  pebbles 
found  in  North  America?  7.  If  you  live  in  the  part  of  North  Amer- 


viii  QUESTIONS   FOB   THE   USE   OF   STUDENTS. 

ica  where  glaciers  have  been,  you  will  find  gravel  heaps  on  the  hill- 
sides and  tops,  and  the  newly  uncovered  bed  rocks  will  be  scratched 
or  smoothed.  Is  this  the  case  in  the  region  where  you  live  ? 

Lesson  IV.    Page  12. 

1.  How  do  sand  grains  differ  from  pebbles?  2.  Describe  the  ap- 
pearance^df  sand.  3.  What  do  we  obtain  if  we  melt  sand?  4.  When 
and  how  is  sand  made  ?  5.  How  does  sand  help  the  streams  to  wear 
the  rocks  ?  6.  How  does  the  sandblast  act  in  carving  glass  ? 

Lesson  V.    Page  15. 

1.  Where  do  we  see  thaf  action  of  sand  the  best  ?  2.  Why  do  not 
the  waves  wear  sand  beaches  very  much?  3.  Under  what  circum- 
stances does  the  sand  get  ground  up  on  the  beach  ?  4.  How  does  the 
sand  escape  from  the  waves  into  the  air?  5.  What  are  dunes? 
6.  Why  are  they  more  common  in  Europe  than  in  America?  7.  Where 
are  they  very  large  ?  8.  What  is  the  effect  of  making  a  hole  in  the 
dunes?  9.  How  does  the  sand  travel  out  to  sea?  10.  Where  is  the 
most  sand  made?  11.  Why  are  there  dunes  on  the  Sahara?  12.  Is 
sand  formed  beneath  glaciers?  13.  What  is  the  effect  of  blown  sand 
on  the  rocks  it  passes  over  ? 

Lesson  VI.    Page  2O. 

1.  Of  what  is  mud  composed  ?  2.  How  is  it  made  ?  3.  How  does 
it  change  in  nature  as  we  go  down  stream  ?  4.  Is  it  formed  on  sea- 
shores? 5.  How  is  mud  made  in  soils?  6.  What  is  the  action  of 
earthworms  ?  7.  Of  plant  roots  ?  8.  Describe  the  several  actions  that 
make  mud. 

Lesson  VII.    Page  24. 

1.  On  what  does  all  the  life  of  the  land  depend?  2.  Describe  a 
soil.  3.  Have  you  ever  noticed  how  a  soil  is  made?  4.  From  what 
things  are  soils  made  ?  5.  How  do  soils  form  on  bare  rock  ?  6.  On 
what  does  the  richness  of  a  soil  depend  ?  7.  Describe  the  action  of 
tillage  on  soils.  8.  How  are  soils  formed  along  rivers?  9.  How  do 
glacial  soils  differ  from  others  ?  10.  Why  do  we  owe  a  duty  by  soils  ? 


QUESTIONS    FOR   THE   USE   OF    STUDENTS.  ix 

CHAPTER   II. 

Lesson  I.    Page  3O. 

1.  When  pebbles  are  connected  together,  what  is  the  rock  called  ? 
2.  What  is  the  millstone  grit?  3.  How  are  the  stones  bound  together? 

4.  How  are  great  quantities  of  pebbles  brought  together?     5.  What 
do  we  learn   from  the  process  of  making  brick?     6.  How  can  the 
rocks  be  made  very  hot  ?     7.  What  changes  of  shape  sometimes  occur 
in  the  pebbles  of  pudding-stones?     8.  Why  do  small  pebbles  last  a 
long  time? 

Lesson  II.    Page  34. 

1.  Of  what  are  sandstones  made  ?  2.  Describe  the  bedding  of 
sandstones.  3.  How  is  cross-bedding  made  ?  4.  Why  are  sandstones 
found  over  so  large  a  part  of  the  world? 

Lesson  III.    Page  36. 

1.  Why  are  the  clay  or  mud  stones  found  over  a  wider  field  than 
the  other  rocks  ?  2.  How  do  volcanoes  help  the  making  of  mud  on 
the  sea-floor  ?  3.  What  is  pumice  ?  4.  Why  can  it  float  very  far  ? 

5.  What  is  the  difference  in  the  rate  of  making  of  claystones  and  sand- 
stones ?     [6.  Does  this  teach  us  any  important  fact  ?] 

Lesson  IV.    Page  38. 

1.  How  do  limestones  differ  from  rocks  previously  described? 
2.  How  are  they  formed?  3.  What  are  coral  reefs?  4.  Where  do 
coral  reefs  abound?  o.  Account  for  their  shapes.  6.  Why  is  a  mo- 
tion of  the  water  necessaiy?  7.  Are  coral  reefs  the  most  powerful 
makers  of  limestone?  8.  What  can  you  say  of  f oraminifera ?  9.  What 
changes  have  been  brought  about  in  certain  limestones  by  the  action 
of  heat?  10.  What  effect  have  these  changes  on  the  animal  remains 
buried  in  the  limestone  ?  11.  How  is  lime  supplied  to  the  sea  to  re- 
place that  which  is  constantly  being  taken  from  it  by  animals? 
12.  How  do  limestones  affect  soils  ?  13.  Describe  the  course  of  matter 
from  land  to  sea  and  from  sea  back  to  land.  [14.  What  is  the  force 
that  brings  about  this  movement?] 

Lesson  V.    Page  46. 

1.  Of  what  does  coal  consist?  2.  Name  the  principal  varieties  of 
coaly  matter.  3.  How  do  plants  obtain  carbon?  4.  What  happens 


X  QUESTIONS   FOR   THE  USE   OF   STUDENTS. 

when  leaves,  branches,  or  trunks  of  trees  fall  to  the  ground  ?  5.  How, 
in  some  cases,  is  the  wood  preserved  from  complete  decay?  6.  Com- 
pare the  process  of  decay  in  a  wet  and  in  a  dry  forest.  7.  What  is 
peat?  8.  How  can  peat  bogs  be  converted  into  coal?  9.  How  has 
coal  been  artificially  made  ?  10.  How  can  anthracite  coal  be  produced 
from  bituminous  coal  ?  11.  What  do  we  see  on  the  coal  field  near 
Kichmond,  Va.  ?  12.  What  was  the  climate  during  the  carboniferous 
period?  13.  Whence  comes  the  heat  that  we  find  in  coal?  14.  How 
long  has  coal  been  in  use?  15.  Where  are  the  largest  coal  fields? 
1G.  How  is  petroleum  formed?  17.  Where  has  it  long  been  gathered? 
18.  Where  is  the  greatest  amount  found?  19.  What  other  form  of 
burnable  matter  is  found  in  the  earth?  [20.  How  does  coal  affect  the 
prosperity  of  nations  *?] 

CHAPTER   III. 

Lesson  I.    Page  56. 

1.  Compare  air  and  ocean.  2.  What  is  the  principal  gas  of  the 
atmosphere  ?  3.  Of  what  sort  of  bits  is  the  air  believed  to  be  com- 
posed ?  4.  How  do  we  know  that  the  air  can  easily  move  ?  5.  How 
do  we  know  that  it  can  take  up  particles  of  water  ?  6.  How  do  we 
know  that  cold  makes  it  heavier  ?  7.  What  is  the  effect  of  the  sun  on 
the  air  at  the  equator?  8.  What  is  the  effect  of  the  lands  on  the 
winds?  9.  What  would  be  the  behavior  of  winds  if  the  earth  were 
all  land  or  all  water?  10.  Describe  currents  of  water  through  air  to 
lands,  thence  back  to  seas.  11.  What  is  one  important  effect? 
12.  How  does  the  air  act  as  a  blanket?  13.  In  what  other  way  does 
air  help  life?  [14.  How  do  we  know  that  the  spaces  of  the  heavens 
are  very  cold  ?] 

Lesson  II.    Page  62. 

1.  Compare  atmosphere  and  oceans.  2.  Describe  work  of  water 
dependent  on  its  dissolving  power.  3.  How  does  water  work  as  a 
means  of  carriage  of  matter?  4.  How  does  it  carry  heat?  5.  What 
would  be  the  effect  if  the  Gulf  Stream  ceased  to  move  ? 

Lesson  III.    Page  66. 

1.  What  are  veins?  2.  How  are  the  crevices  formed?  3.  How  are 
they  filled?  4.  What  valuable  substances  are  found  in  them?  5.  De- 
scribe some  like  deposits  not  in  vein  crevices.  6.  Describe  the  way  in 


QUESTIONS   FOR    THE   USE   OF    STUDENTS.  XI 

which  metals  from  veins  may  pass  to  the  sea.  7.  How  may  the 
metal  then  be  fixed  to  the  mud  ?  8.  In  what  other  way  may  fractures 
in  the  rock  be  filled?  9.  How  do  dykes  differ  from  lava  streams? 
[10.  How  does  the  possession  of  metals  affect  man  ?] 

Lesson  IV.    Page  74. 

1.  Describe  the  two  ways  in  which  rain  water  goes  away  from  the 
point  where  it  fell.  2.  Describe  springs.  3.  What  may  be  said  of 
the  underground  course  of  strong  springs  ?  4.  What  rocks  most 
favor  the  making  of  large  springs  ?  5.  What  are  caverns  ?  6.  Where 
are  the  largest  found  ?  7.  What  is  the  nature  of  the  surface  of  a 
country  beneath  which  caverns  are  found?  8.  What  are  sink-holes, 
galleries,  and  domes?  9.  How  are  the  domes  formed?  10.  How  do 
stalactites  form  ?  11.  How  do  they  close  the  gallery  ?  12.  What  are 
natural  bridges?  13.  What  is  there  remarkable  about  the  animals  of 
caves?  14.  What  are  the  movements  of  air  into  and  out  of  the 
cavern  due  to?  15.  How  are  the  remains  of  animals  preserved  in 
caves?  16.  What  other  sorts  of  caves  occur,  and  how  are  they 
formed?  17.  What  is  a  "spouting  horn"? 


CHAPTER   IV. 

Lesson  I.    Page  88. 

1.  What  part  of  the  earth  is  known  to  us  by  sight?  2.  What  is  a 
volcano?  3.  What  gas  is  most  plentiful  in  volcanic  eruptions? 

4.  Where  are  volcanoes  found?     5.   How   do  volcanoes  originate? 
(5.  What  volcanoes  are  best  known  to  us?     7.  Describe  the  eruption  of 
Vesuvius  in  79.     8.  What  cities  were   buried?     9.  Where   is  Strom- 
boli?     10.  Describe  the  flow  of  a  lava  stream.     11.  What  lava  streams 
do  we  find  in  California?     12.  What  part  do  volcanoes  take  in  the 
world's  machinery? 

Lesson  II.    Page  98. 

1.  What  are  the  two  forms  of  the  earth's  life?  2.  Whence  come 
almost  all  its  motions  ?  3.  What  would  be  the  effect  of  cutting  off 
the  heat  of  the  sun  ?  4.  In  what  way  does  the  sun's  force  come  to  us  ? 

5.  What  part  comes  from  the  fixed  stars  ?     6.  What  part  of  the  earth 
receives  the  most  of  the  sun's  heat?     7.  What  would  happen  if  the 
sun's  heat  stayed  where  it  fell  ?    8.  What  is  the  effect  of  the  storage 


Xll  QUESTIONS   FOK   THE   USE   OF   STUDENTS. 

of  heat?  9.  How  does  water  carry  heat  away  from  the  equator? 
10.  What  does  a  paper  balloon  show  us?  11.  How  can  we  compare 
the  circulation  of  the  atmosphere  with  the  movement  of  the  air  about 
a  heated  stove?  12.  How  would  the  winds  move  if  the  earth  stood 
still  on  its  axis?  13.  Why  do  the  winds  tend  to  the  west  in  going- 
south  and  to  the  east  in  going  north  ?  14.  How  can  this  be  illus- 
trated? 15.  How  do  the  trade  winds  produce  the  ocean  currents? 
16.  In  what  courses  do  these  currents  of  the  sea  move?  17.  How  do 
the  waters  return  to  the  equator?  18.  How  do  the  shapes  of  the 
lands  influence  the  sea  currents?  19.  What  would  be  the  effect  of 
lowering  Alaska  and  the  Aleutian  Islands  beneath  the  sea?  20.  What 
are  the  other  causes  of  changes  in  the  climate  ?  [21.  What  do  you 
understand  by  climate  ?] 

CHAPTER  V. 

Lesson  I.    Page  1O7. 

1.  What  are  hills?  2.  How  do  they  differ  from  mountains  ?  3.  How 
do  the  beds  of  rock  lie  in  mountains?  4.  To  what  are  mountains 
due?  5.  What  causes  the  crust  to  wrinkle?  6.  How  do  we  know 
that  most  things  shrink  in  losing  heat  ?  7.  How  do  we  know  that 
most  mountains  rise  slowly?  8.  What  are  the  Alleghenies  like? 
9.  How  do.  they  differ  from  the  Alps  ?  10.  What  happens  when 
mountains  cease  to  grow?  11.  What  help  do  mountains  give  to  those 
who  seek  the  minerals  of  the  earth  ?  12.  How  much  do  the  folds  in 
the  rocks  differ  in  size?  13.  How  do  continental  folds  differ  from 
those  of  mountains  ?  [14.  What  is  the  striking  difference  between  the 
movement  of  heat  from  the  earth's  crust  and  that  to  the  earth's  crust 
from  the  sun?] 

CHAPTER   VI. 
Lesson  I.    Page  113. 

1.  What  should  we  observe  in  order  to  see  how  valleys  are  formed  ? 
2.  What  happens  when  the  lands  rise  out  of  the  sea?  3.  What  are 
the  principal  parts  of  a  river  valley?  4.  What  do  we  see  in  a  moun- 
tain stream?  5.  What  change  is  marked  when  the  stream  has  less 
fall?  6.  How  is  the  alluvial  plain  made?  7.  What  is  the  delta? 
8.  How  are  falls  formed?  9.  How  is  Niagara  formed?  10.  How  the 
Ohio  falls?  11.  What  are  "oxbows"?  "moats"?  12.  How  are  ter- 


QUESTIONS   FOR   THE   USE   OF   STUDENTS.  Xlll 

races  formed?  13.  How  are  canons  (pronounced  canyons)  formed? 
14.  Where  is  the  best  example?  15.  How  was  the  Yosemite  Valley 
formed?  16.  How  are  tidal  valleys  formed?  17.  Where  are  good 
examples  ?  18.  How  do  tides  affect  animal  life  ? 

Lesson  II.    Page  125. 

1.  What  can  be  said  of  the  way  in  which  lakes  are  placed? 
2.  What  are  the  important  divisions  of  lakes?  3.  Why  are  certain 
lakes  salt?  4.  What  of  salt  deposits?  5.  How  were  most  of  the  lake 
basins  north  of  40°  latitude  formed  ?  6.  What  sort  of  a  surface  was 
given  to  the  land  by  the  glaciers,  and  why?  [7.  Why  does  a  lake 
last  but  a  short  geological  time?]  [8.  What  will  in  time  happen  to 
the  American  Great  Lakes  ?] 

CHAPTER  VII. 
Lesson  I.    Page  ISO. 

1.  Describe  the  events  of  the  Lisbon  earthquake.  2.  What  are  the 
three  forms  of  danger  in  earthquakes  ?  3.  Describe  the  great  Missis- 
sippi earthquake  of  1811.  4.  What  are  the  worst  regions  for  earth- 
quakes? 5.  What  action  of  the  earth  may  produce  the  jarring 
motion  of  an  earthquake  ?  6.  What  effect  does  it  have  on  the  ani- 
mals of  the  sea?  7.  How  does  it  produce  great  waves?  8.  What  is 
the  effect  of  these  waves? 

Lesson  II.    Page  141. 

1.  What  is  the  best  proof  that  the  lands  have  once  been  sea-floors  ? 
2.  What  can  be  said  about  a  lift  on  the  Chilian  shore?  3.  How  does 
the  sea  take  the  lands  back  to  itself  ?  4.  What  would  happen  if  the 
Isthmus  of  Darien  were  to  be  lowered  beneath  the  sea?  5.  What 
would  be  the  effect  of  lifting  the  Malay  Archipelago  so  that  a  land 
bridge  from  Asia  to  Australia  should  be  formed  ?  [6.  What  is  the 
effect  of  moving  animals  to  new  countries?] 

CHAPTER  VIII. 
Lesson  I.    Page  146. 

1.  Whence  comes  the  force  that  acts  in  organic  life  ?  2.  What  are 
some  of  the  effects  cf  life  on  the  earth?  3  What  is  the  best  proof  of 


Xiv  QUESTIONS   FOE   THE   USE   OF   STUDENTS. 

the  perfection  of  the  earth's  machinery  ?     [4.  Is  it  reasonable  to  sup 
pose  that  this  order  is  due  to  chance  ?] 

Lesson  II.    Page  149. 

1.  By  what  marks  are  organic  beings  separated  from  the  inanimate 
world?  2.  Give  the  names  of  four  animals  that  are  closely  akin. 
3.  Why  are  these  akin?  4.  Give  a  list  of  some  not  closely  akin. 
5.  What  are  the  contrivances  for  measuring  time?  6.  In  what  order 
of  relations  can  you  place  them  ?  7.  How  many  plans  of  animal 
structure  can  you  name?  [8.  Can  you  classify  a  bee  or  a  beetle  ?] 

CHAPTER   IX. 

Lesson  I.    Page  155. 

1.  Contrast  living  things  with  things  that  have  not  life.  2.  Why 
is  there  no  gradual  passage  from  the  mineral  to  the  living  world? 
3.  What  are  the  lowliest  organized  creatures  like?  4.  What  were  the 
first  plants?  5.  What  is  the  most  marked  difference  between  animals 
and  plants?  6.  What  do  plants  strive  to  do  in  their  successive 
changes?  7.  Compare  a  rose-bush  and  a  sea-weed.  8.  What  are 
these  changes  for?  9.  What  are  the  changes  in  the  seed?  10.  What 
purpose  do  flowers  and  fruits  serve?  11.  How  do  the  purposes  of 
animals  differ  from  those  of  plants  ?  12.  What  is  the  machinery  of 
intelligence  in  an  animal? 

Lesson  II.    Page  164. 

1.  What  are  protozoa  like?  2.  What  are  radiates  like?  3.  What 
are  the  lowest  radiates?  4.  What  the  highest?  5.  WThat  about  their 
motion?  6.  What  about  their  nervous  systems?  [7.  What  about 
their  intelligence?] 

Lesson  III.    Page  168. 

1.  Name  some  bivalve  mollusks.  2.  How  do  they  differ  from 
radiates?  3.  What  forms  of  bivalves  move?  4.  Name  some  single- 
shelled  mollusks.  5.  Why  are  they  higher  in  structure  than  the 
bivalves?  6.  What  are  the  lowest  land  animals?  7.  How  do  the 
squids  differ  from  snails?  8.  Why  are  they  higher  than  snails? 
9.  How  do  they  move?  10.  What  of  their  nervous  system?  11.  Why 
are  mollusks  as  a  whole  higher  animals  than  the  radiates  ? 


QUESTIONS   FOR   THE   USE   OF   STUDENTS.  XV 

Lesson  IV.    Page  175. 

1.  Name  some  articulates.  2.  How  are  they  built?  3.  How  do 
the  worms  differ  from  the  crustaceans?  4.  How  does  an  insect  differ 
from  a  crab?  5.  Give  the  names  of  a  dozen  different  kinds  of  in- 
sects? 6.  How  do  the  minds  of  insects  differ  from  those  of  the  lower 
animals?  [7.  What  is  the  reason  they  do  not  have  a  more  important 
place  in  the  world  ?]  8.  Compare  the  articulates  with  the  mollusks 
and  the  radiates. 

Lesson  V.    Page  179. 

1 .  What  is  the  highest  of  the  great  groups  of  animals  ?  2.  Why  is 
it  the  highest?  3.  What  are  the  peculiar  features  of  the  fishes? 
4.  What  are  the  amphibians?  5.  What  changes  do  they  undergo? 
6.  What  are  the  reptiles?  7.  What  power  of  motion  do  they  have? 
8.  How  do  the  birds  differ  from  the  reptiles  ?  9.  What  is  the  advan- 
tage of  warm  blood?  10.  What  is  the  highest  group  of  animals? 
11.  How  is  it  distinguished?  12.  What  are  the  lowest  of  the  mam- 
mals? 13.  Describe  the  advantages  of  the  vertebrate  skeleton. 
14.  How  does  the  nervous  system  of  vertebrates  show  itself  better 
built  than  in  lower  animals  ?  15.  How  do  vertebrates  give  help  to 
their  young  ?  16.  Tell  the  succession  of  coming  into  life  of  the  vari- 
ous groups  of  vertebrates.  17.  When  do  the  vertebrates  first  appear 
on  the  earth?  18.  How  do  the  means  of  speech  in  vertebrates  com- 
pare with  those  of  lower  animals?  19.  How  does  man  differ  from 
the  lower  animals?  20.  How  is  he  related  to  them?  [21.  How  does 
his  mind  differ  from  the  animal  mind?] 

CHAPTER  X. 

Lesson  I.    Page  189. 

1.  What  animals  leave  no  remains  on  the  rocks?  2.  What  be- 
comes of  hard  parts  if  they  are  left  uncovered  on  the  surface  of  the 
earth?  3.  What  do  we  find  in  an  old  forest?  4.  What  are  the  ways 
in  which  animals  may  become  buried  on  the  land?  5.  Why  are 
fossils  more  often  formed  on  the  sea  than  on  the  land?  6.  How  are 
fossils  preserved?  7.  How  are  they  changed  after  they  become  deeply 
buried?  8.  Of  what  use  are  fossils  to  the  geologist?  9.  What  do 
they  tell  him?  [10.  What  part  of  all  the  life  that  the  earth  has  borne 
has  been  fossilized?] 


XVi  QUESTIONS   FOR   THE   USE   OF   STUDENTS. 

CHAPTER  XL 

Lesson  I.    Page  195. 

1.  How  long  have  we  known  that  life  was  a  very  ancient  thing  in 
the  world?  2.  Why  must  we  believe  that  existing  animals  have 
sprung  from  the  more  ancient  kinds  that  once  existed,  but  no  longer 
live?  3.  What  does  the  Darwinian  theory  suppose?  4.  What  do  we 
find  among  our  domestic  animals  that  helps  us  to  understand  the 
changes  of  animals?  5.  How  do  we  know  that  life  may  become 
degraded  as  well  as  advanced?  [6.  Is  there  any  similar  truth  in 
morals?] 

Lesson  II.    Page  2O3. 

1.  How  do  conglomerates  or  pudding-stones  and  sandstones  show 
that  the  earth  is  old?  2.  How  do  limestones  show  it?  3.  What  do 
we  learn  from  water-falls?  4.  From  the  peninsula  of  Florida? 
5.  From  the  elevation  of  certain  countries?  6.  How  does  the  history 
of  life  show  us  that  the  earth  is  very  old?  7.  How  can  we  represent 
the  earth's  age  in  years  by  distance  in  feet  ?  8.  How  do  the  beds  of 
rock  give  us  clews  to  the  history  of  the  earth?  9.  How  many  years  of 
life  can  you  remember?  10.  What  part  is  this  of  1,000,000  years? 

CHAPTER  XH. 

Lesson  I.    Page  209. 

1.  What  was  probably  the  first  condition  of  the  earth?  2.  What 
do  we  learn  from  the  planet  Saturn  ?  3.  How  was  the  heat  of  the 
earth  developed?  4.  When  did  the  water  of  the  seas  come  upon  the 
earth? 

Lesson  II.    Page  213. 

1.  What  are  the  oldest  rocks  called  ?  2.  Where  do  we  find  the  first 
certain  evidences  of  life?  3.  What  animals  were  there  in  the  seas? 
4.  What  higher  animals  were  wanting?  5.  What  change  in  life 
marks  the  Devonian  period?  6.  What  marks  the  carboniferous  age? 
7.  What  important  groups  of  animals  appeared  then  ?  8.  What  im- 
portant groups  of  animals  appear  in  the  Triassic  age?  9.  What  do 
the  Connecticut  Valley  footprints  teach  us  ?  10.  When  did  the  first 
mammals  appear?  11.  What  were  they  like?  12.  What  do  the  salt 
deposits  of  the  Triassic  time  teach  us  ?  13.  What  were  the  reptiles 


QUESTIONS   FOR   THE   USE   OF   STUDENTS.  xvii 

of  the  Reptilian  period  like?  14.  When  do  the  birds  first  appear? 
15.  How  did  they  differ  from  our  living  birds  ?  16.  What  advance 
took  place  in  the  plants  of  this  time?  17.  Wliat  changes  in  the  land 
took  place  in  the  Cretaceous  period?  18.  When  did  the  broad-leaved 
trees  begin?  19.  In  passing  from  the  Cretaceous  to  the  Tertiary 
period,  what  was  the  great  change  in  life?  20.  Is  it  likely  that  these 
new  forms  of  animals  were  suddenly  created?  21.  What  common 
forms  of  animals  were  wanting  in  the  lower  Tertiary?  22.  What  was 
the  nature  of  the  mass  of  mammals  at  that  time?  23.  What  were  the 
successive  changes  by  which  the  five-fingered  foot  became  changed 
into  a  horse's  foot?  24.  What  are  the  splint  bones  of  the  horse's  foot? 
25.  What  can  be  said  about  the  advance  of  birds  during  the  Ter- 
tiary period?  26.  What  about  advance  in  the  insects?  27.  What 
about  advance  in  the  cephalopods?  28.  What  advance  is  seen  in  the 
plants? 

APPENDIX. 

Crystalline  Rocks.    Page  233. 

1.  What  are  the  three  physical  states  of  matter?  2.  In  which  state 
do  crystals  occur?  3.  Give  some  instances  of  crystals.  4.  What  can 
be  said  of  the  shape  of  crystals  of  any  one  substance?  5.  What  do 
meteors  show  us?  6.  What  do  we  find  in  little-changed  stratified 
rocks?  7.  How  are  crystalline  rocks  made? 

1.  What  is  claystone?  2.  How  is  slaty  cleavage  made?  3.  How 
is  limestone  marble  made?  4.  What  is  the  change  that  may  be 
made  in  sandstone?  5.  What  are  dykes?  6.  What  are  veins? 
7.  Give  the  important  points  about  the  following  minerals:  quartz, 
felspar,  mica,  hornblende,  pyroxine,  calcite,  dolomite,  gypsum,  com- 
mon salt,  pyrite,  magnetite,  hematite,  limonite,  siderite,  copper,  zinc, 
tin,  gold,  aluminium,  sulphur.  8.  Of  what  minerals  are  the  following 
rocks  composed:  granite,  syenite,  gneiss,  mica  schist,  porphyry,  stea- 
tite, turpentine,  quartzite?  9.  How  are  these  rocks  and  crystals  de 
stroyed?  10.  How  do  they  return  to  the  crystalline  state? 


CHAPTER   I. 


PEBBLES,    SAND,   AND   CLAT. 


LESSON  I. 
RIVER    PEBBLES. 

F  ET  us  take  a  number  of  pebbles  such  as  come  from  the 
-*-^  bed  of  a  river.  We  notice  that  they  are  of  different 
shapes  and  of  different  colors  and  of  many  sizes.  They  are 
all  hard  and  smooth,  but  some  are  smoother  than  others ; 
some  have  faces- that  are  nearly  flat,  and  some  are  almost 
as  round  as  marbles ;  some  are  all  of  the  same  sort  of  stone, 
and  others  are  made  up  of  several  different  kinds  of  stone 
mingled  together.  If  we  could  see  the  way  in  which  these 
pebbles  were  formed,  we  should  know  much  of  the  history 
of  the  world. 

Let  us  trace  the  history  of  these  pebbles  back  into  the 
past.  It  is  a  long  story ;  for,  between  the  time  their  mak- 
ing began  and  the  hour  in  which  they  were  taken  from 
the  water,  a  vast  length  of  years  has  gone  by.  If  we  look 
at  the  stream-bed  where  these  pebbles  were  found,  we  find 
that  it  is  so  full  of  them  that  its  bottom  and  sides  are  in 
good  part  made  up  of  such  bits  of  stone.  When  they  were 
taken  out,  they  were  slowly  working  down  towards  the 
sea.  Every  flood  rolled  them  a  little  farther  on  their  way, 
and  were  it  not  for  the  fact  that  they  are  from  time  to 
time  caught  on  the  sides  of  the  stream,  and  held  by  the 
other  stones  laid  on  top  of  them,  or  tied  by  the  roots  of 


2  PEBBLES,  SAND,  AND  CLAY. 

plants,  they  would  travel  only  a  few  years  before  they 
would  be  either  worn  out  by  the  bruising  they  received 
on  their  rough  journey,  or  rolled  into  the  sea.  But  if  we 
examine  the  banks  of  either  side  of  the  river,  we  find  that 
there  are  great  quantities  of  such  pebbles  as  are  now  in  the 
stream,  that  have  been  stopped  in  their  journey,  and  built 
into  the  strip  of  level  land  that  makes  a  plain  on  either 
side  of  the  river.  The  chance  was,  that  if  these  pebbles 
had  been  left  where  they  were  found,  they  too  would  have 
often  been  compelled  to  wait  on  the  bank;  because  the 
stream  does  not  always  keep  the  same  bed,  but  is  continually 


Firj.  1. 

Section  across  River  Valley. 

cutting  away  on  one  side  and  filling  in  on  the  other.  So 
that  each  pebble  journeys  a  little  way  down  stream,  and 
then  rests  awhile  on  the  bank ;  while  other  pebbles,  that 
have  been  perhaps  for  thousands  of  years  imprisoned  in  the 
bank,  are  taken  out  by  the  changing  river  and.  carried  a 
way  down  stream,  again  to  be  put  into  their  resting-places 
on  the  alluvial  land. 

Let  us  look  for  the  place  where  these  pebbles  were 
found.  As  we  go  up  stream  we  find  the  pebbles  growing 
always  larger  and  more  angular,  until  at  length  we  find 
them  so  heavy  that  only  the  swiftest-running  waters  can 
move  them ;  this  is  because  they  wear  away  by  rolling 


RIVER  PEBBLES.  8 

over  each  other.  This  work  is  copied  in  the  making  of 
boys'  marbles ;  and  it  is  worth  while  to  notice  how  in  this, 
as  in  many' other  branches  of  labor,  man  succeeds  in  his 
tasks  by  imitating  Nature.  In  making  marbles,  bits  of 
square  stone,  all  of  about  the  same  size  and  of  even  hard- 
ness, are  put  into  a  large  drum  through  which  a  stream  of 
water  flows.  This  drum  turns  around  like  a  wheel,  causing 
the  stones  to  rub  over  each  other ;  the  same  amount  of 
wear  being  given  to  every  side,  they  come  out  spheres.  It 
might  seem  at  first  that  we  ought  to  have  the  same  shapes 
in  the  river-pebbles,  but  we  notice  that  these  are  usually  a 
little  larger  one  way  than  they  are  the  other ;  they  are 
often  so  flattened  that  they  are  called  "shingle."  This  is 
because  stones  are  generally  more  easily  worn  in  one  direc- 
tion than  in  the  others.  They  are  not  equally  soft  on  all 
sides.  If  we  should  turn  them  round  on  a  lathe,  and  then 
put  them  in  the  marble-maker's  drum,  they  would  wear 
into  oblong  shapes.  As  soon  as  a  stone  is  a  little  flattened, 
the  water  finds  it  easier  to  push  it  along  on  its  side  than  to 
roll  it  over  and  over ;  so  it  wears  it  into  the  thin  shapes  we 
often  find. 

Going  up  the  stream,  we  come  to  trie  part  of  its  course 
where  it  no  longer  makes  its  bed  in  gravel  and  sand,  but 
tumbles  over  the  hard  rocks.  Here  we  can  see  the  place 
where  the  making  of  the  pebbles  begins.  We  see  large 
masses  of  stone  that  have  been  broken  out  of  the  cliffs 
that  border  the  streams.  These  bits  are  of  all  sizes :  some 
of  them  so  small  that  the  stream  sends  them  bowling  along 
down  its  bed ;  others  great  masses  as  large  as  a  barrel,  or 
larger,  that  lie  still  in  its  bed,  and  force  the  water  to  turn 
out  of  its  way.  When  these  great  masses  of  stone  are  very 
solid,  they  may  last  for  centuries  without  being  harmed  by 
the  stream ;  but  usually  there  are  some  very  slight  crevices 


4  PEBBLES,  SAXD,  AND  CLAY. 

in  the  stone  into  which  the  water  finds  its  way.  During 
the  summer  season  the  water  can  do  but  little,  but  when 
the  intense  cold  of  winter  comes,  and  all  the  stream  is 
frozen  to  its  bottom,  this  water  in  the  crevice  also  freezes, 
and  in  so  doing  exerts  power  enough  to  split  the  stone 
in  two.  This  force  the  ice  has  because  water  in  freezing 
must  expand  by  one-seventh  its  bulk ;  to  get  this  greater 
space  it  will  push  tilings  apart  slowly,  but  with  all  the 
force  of  gunpowder.  A  bomb-shell  can  be  broken  by  nil- 
ing  it  with  water,  plugging  up  the  hole  with  an  iron  screw, 
and  putting  it  out  of  doors  of  a  winter's  night  when  the 


Section  down  a  River  Bed. 


thermometer  goes  below  zero.  We  often  see  how  power- 
ful it  is  from  the  bursting  of  frozen  water-pipes. 

This  rending  by  the  frost  will  soon  break  up  most  rocks 
to  bits  that  the  river  in  its  flood-times  can  drive  down 
its  bed.  But  generally  the  stream  grows  less  swift  as  it 
descends  toward  the  sea,  so  that  the  stone  is  urged  for- 
ward with  less  force  than  is  necessary  to  move  it.  When 
this  happens,  it  lies  awhile  until  the  frosts  of  other  winters 
have  divided  it  again. 

It  is  this  same  frost  that  does  the  most  of  the  work  of 
breaking  the  stones  out  of  the  cliff  sides,  so  that  they  may 
tumble  into  the  brook* 


SEA    PEBBLES. 


LESSON    II. 
SEA    PEBBLES. 

WE  have  now  seen  the  most  common  way  in  which  peb- 
bles are  formed ;  but  there  is  another  pebble-mill  on  the 
sea-shore  that  does  much  the  same  sort  of  work,  though  it 
makes  pebbles  of  a  somewhat  different  form. 

If  we  go  to  the  coast  anywhere  where  the  shore  follows 
the  wide  sea,  or  around  a  lake  large  enough  to  form  great 


Fig.  3.    Section  of  a  Cliff  Sea-shore. 

waves, — on  these  coasts  we  find  two  sorts  of  shores:  when 
the  hard  rocks  jut  out  into  the  sea,  there  are  steep  cliffs 
against  which  the  waves  beat  (see  Fig.  3 ) ;  but  the  larger 
part  of  the  shore  is  shelving,  being  made  of  pebbles  and 
sand.  These  shelving  shores  are  called  "  beaches."  They 
are  of  the  form  shown  in  the  figure  (see  Fig.  4).  As  we 
stand  on  these  shores  we  see  that  the  waves,  as  they  break 
upon  it,  run  up  the  beach  with  great  power,  and  then  hurry 
back  only  to  rush  again  up  the  slope  and  again  return.  If 
the  waves  be  strong,  this  swashing  to  and  fro  carries  the 


6  PEBBLES,    SAND,   AND   CLAY. 

water  very  swiftly  up  and  down  the  slope  ;  and,  as  it  goes, 
it  rolls  the  pebbles  with  it.  In  heavy  storms,  stones  as  big 
as  a  man's  head  are  easily  rolled  to  and  fro  for  two  or  three 
hundred  feet  of  distance.  In  these  storms,  the  smaller 
pebbles  are  often  flung  out  with  the  foam  beyond  the 
sweep  of  the  wave,  making  the  ridge  shown  in  the 
picture. 

But  most  of  the  pebbles  of  the  beach  swing  to  and  fro 
within  the  waves  until  they  are  ground  to  the  finest  bits. 
They  are  in  a  mill  that  never  stops  working.  Although 
in  the  course  of  ages  the  shore  moves  about,  it  is  really 


Fir/.  4. 
Section  of  a  Sea  Beach. 

among  the  most  enduring  things  of  the  world ;  for  the  waves 
of  the  sea  have  rolled  in  this  fashion  against  the  land  ever 
since  the  seas  were  made.  A  pebble  on  the  beach,  unless 
it  gets  covered  up  by  other  pebbles,  wears  away  very  fast. 
It  travels  in  times  of  calm  a  little  distance  every  time  the 
wave  strikes ;  as  this  is,  say,  six  times  a  minute,  the  stones 
move  a  few  feet  (we  may  average  the  distance  at  ten 
feet)  in  all  weathers;  they  would  thus  travel  between 
twelve  and  fifteen  miles  a  day.  We  have  only  to  listen, 
as  the  waves  rush  up  and  down,  to  hear  the  grinding 
of  the  pebbles  against  each  other  as  they  are  rolled  to 
and  fro.  It  is  not  only  the  top  pebbles  that  roll,  but  the 


SEA   PEBBLES. 


whole  of  the  beach  is  moved  to  the  depth  of  two  or  three 
feet.  Sometimes  the  roar  of  the  grinding  stones  can  be 
heard  several  hundred  feet  away  from  the  beach. 

The  ground-up  pebbles  make  sand  and  mud,  the  history 
of  which  we  shall  follow  hereafter.  We  will  now  go  seek- 
ing for  the  origin  of  the  beach  pebbles,  as  we  sought  it 
in  ascending  the  stream  when  we  were  finding  the  way  in 
which  river  pebbles  came  to  be.  Nearly  all  beaches  of  the 
sea-shore  are  crescent-shaped,  as  in  Fig.  4;  they  have  at 
one  or  both  ends  of  the  horns  the  place  where  the  peb- 
bles begin  to  be  made.  We  find  these  smallest  in  the 
bottom  of  the  hollow,  and 
they  grow  larger  as  we  pass 
out  toward  the  place  where 
they  begin  to  form;  just  as 
they  grew  larger  as  we  went 
up  the  stream  when  looking 
for  the  place  whence  the  river 
pebbles  came.  When  we  get 
to  the  end  of  the  beach  we  find 
the  beating  sea-waves  at  work  &a- 5-  MaP  of  a  Sea  Beach- 
cutting  out  the  stones  of  which  the  pebbles  are  to  be  made. 
If  the  rock  be  as  soft  as  a  gravel  bank  is,  and  many  of  the 
beaches  of  our  northern  coast  are  cut  in  gravelly  beds,  the 
sea  has  little  work  to  do ;  the  waves  soon  cut  back  into  the 
cliff,  when  the  overhanging  mass  slips  down  into  the  sea ;  then 
the  pebbles  are  driven  on  to  the  beach,  when  their  rolling  to 
and  fro  begins.  But  when  the  rocks  are  hard,  the  sea  has  a 
good  deal  of  work  to  do  to  force  out  the  blocks  of  stone ;  but 
by  taking  those  on  which  it  gets  a  grip,  and  hurling  them 
against  the  rock,  it  slowly  but  surely  manages  to  cut  back 
a  groove  so  that  the  rocks  overhang  and  fall  of  their  own 
weight.  When  they  fall,  these  masses  of  rock  generally 


8  PEBBLES,  SAND,  AND  CLAY. 

break  up  into  pieces  that  the  waves  can  lift  and  hurl 
against  the  cliff,  or  against  each  other,  until,  by  breaking, 
they  become  small  enough  to  be  kept  in  constant  motion : 
then  they  are  quickly  crushed  into  pebbles,  and  rolled  to 
the  beach.  Thus,  the  cliff  part  of  the  shore  feeds  the  sea- 
beach,  which  is  a  sort  of  mill  for  grinding  pebbles. 

LESSON  III. 

GLACIAL    PEBBLES. 

THERE  is  a  third  kind  of  pebble  that  has  a  different  his- 
tory from  either  of  the  other  two.  It,  too,  is  the  work  of 
water,  but  of  water  working  in  the  very  different  form 
of  ice.  In  the  regions  near  the  poles  of  the  earth,  and  in 
the  high-up  valleys  of  some  great  mountains,  we  have  snow 
that  never  melts  from  one  year  to  another.  This  snow 
would  make  an  immensely  high  mass  if  it  had  no  way  to 
escape  ;  but  a  road  for  it  to  get  into  warmer  regions  where 
it  can  melt  is  provided  in  this  way :  — 

The  eternal  snow-fields  are  always  receiving  snow  both 
in  summer  and  winter.  This  snow  is  pressed  down  by 
that  which  falls  upon  it,  and  by  this  pressure  is  turned 
into  ice.  We  easily  see  how  much  harder  and  ice-like 
snow  grows  when  pressed.  A  snow-ball,  if  squeezed  hard, 
becomes  a  whitish  ice,  and  the  snow  that  gathers  on  our 
feet  is  almost  as  hard  as  ice.  Now,  a  great  mass  of  this 
hardened  snow,  lying  on  the  sloping  ground  of  the  moun- 
tains, will  flow  down  that  slope,  becoming  more  like  pure 
ice  as  it  goes  downward.  When  it  gets  into  the  lower 
valleys,  it  is  a  true  river  of  ice,  that  may  be  half  a  mile  or 
more  wide,  and  hundreds  of  feet  deep.  In  the  Alps  and 
Himalayas  these  streams  slowly  creep  for  miles,  some- 
times for  as  much  as  thirty  miles,  down  the  valleys,  until 
they  come  to  regions  warm  enough  to  melt  them  away. 


GLACIAL   PEBBLES.  9 

These  streams  of  ice  are  called  "glaciers,"  from  the  French 
word  glace,  which  means  ice.  They  move  very  slowly,  not 
more  than  three  or  four  feet  a  day.  They  are  constantly 
breaking  and  soldering  together,  but  still  they  move  on, 
faster  in  summer  and  slower  in  winter,  and  so  drain  away 
the  snow  from  the  regions  where  it  cannot  melt.  Out 
from  beneath  these  glaciers  there  flows  a  stream.  Its 
water  is  always  very  muddy,  and  it  bears  away  many 


Fig.  6. 
Section  down  a  Glacier. 

pebbles,  which,  with  the  rocks  that  have  been  carried  on 
the  surface  of  the  ice,  make  great  masses  of  stones  called 
"  moraines." 

If  we  look  closely  at  these  pebbles,  we  may  see  that, 
though  they  somewhat  resemble  those  from  the  rivers  and 
the  sea-shore,  they  are  yet  unlike  them.  These  stones 
shaped  beneath  the  ice  are  not  so  smooth  and  round  as 
the  others ;  they  often  have  scratches  upon  them,  as  in 
the  figure,  which  show  that  they  have  been  held  fast 
in  the  ice  and  pushed  over  some  hard  substance.  (Fig.  7.) 
We  can  see  the  way  these  scratches  are  formed  if  we  enter 
the  cave  out  of  which  flows  the  stream  that  drains  the 
glacier,  and  find  a  place  where  the  ice  rests  on  the  rock. 


10  PEBBLES,  SAND,  AND  CLAY. 

This  we  can  easily  do  on  many  a  glacier.  When  the  ice 
rests  on  the  rock,  we  often  find  that  it  has  grasped  pebbles 
that  are  held  firmly  upon  the  rock  and  forced  along  over 
it.  As  the  ice  slowly  melts  when  it  touches  the  rock, 
because  of  the  heat  of  the  earth  and  the  heat  that  comes 
from  the  rubbing  that  takes  place  there,  these  stones  are 
pressed  on  by  all  the  ice  above  them,  so  that  a  stone  as 
big  as  an  apple  may  have  many  tons  of  weight  upon  it. 

These  pebbles  scratch  the  stone  over  which  they  are 
pushed,  and  in  turn  are  scratched;  and  so,  when  they 
escape  at  the  end  of  the  glacier,  they  generally  bear  the 


Fig.  1.    Rock  surfaces  scratched  by  Glaciers. 

marks  of  their  struggle  with  the  ice  and  rock.  It  is  not 
every  pebble  that  has  been  under  the  ice  that  bears  these 
marks,  for  there  are  many  that  never  get  caught  in  this 
way,  but  are  carried  on  by  the  stream  that  flows  below 
the  ice,  or  held  up  in  the  ice  so  that  they  are  not  against 
the  rock. 

These  pebbles  are  made  out  of  bits  of  stone  torn  out  of 
the  rock-bed  over  which  the  glacie*r  flows,  or  that  fall  from 
the  rocky  sides  of  the  mountain  upon  the  surface  of  the 
ice,  and  then  find  their  way  through  the  cracks  in  the  ice 
to  the  bed  of  the  glacier. 

Figure  6  shows  an  ice  stream,  with  the  heaps  of  stone 


GLACIAL   PEBBLES.  11 

upon  it  that  have  fallen  from  the  sides  of  the  mountains, 
and  which  very  often  find  their  way  down  into  the  pebble 
factory  at  the  base  of  the  glacier. 

The  muddiness  of  the  water  flowing  from  beneath  gla- 
ciers is  noteworthy.  This  mud  is  made  in  the  grinding 
of  pebbles  and  sand  in  the  way  that  we  have  seen.  There 
is  so  much  of  it  that  every  river  in  Switzerland  which  has 
glaciers  on  its  headwaters  is  very  muddy,  while  those  that 
flow  from  lower  mountains  that  have  no  ice  streams  are 
of  crystal  purity. 

We  have  now  seen  how  the  pebbles  are  made  beneath 
glaciers,  and  the  reasons  why  they  are  more  angular  than 
those  made  by  flowing  water.  We  can  easily  believe  that 
these  scratched  pebbles  tell  an  important  story  when  we 
find  them  in  countries  where  there  are  at  present  no 
glaciers.  As  there  is  no  other  possible  way  in  which  peb- 
bles can  be  so  scratched,  we  may  be  sure  that  wherever  we 
find  them  thus  marked  they  show  that  glaciers  once  ex- 
isted. Now,  such  scratched  pebbles  exist  over  a  large 
part  of  North  America  and  Europe,  and  other  countries 
where  there  is  now  no  trace  of  glaciers.  If  we  take  a  line 
from  New  York  City  through  Pennsylvania,  and  thence 
across  the  continent  to  St.  Paul,  Minn.,  then  to  the  Black 
Hills,  then  south  to  the  Rocky  Mountains  of  Southern 
Colorado,  then  to  the  sea-shore  at  the  mouth  of  the  Colum- 
bia River,  we  may  almost  always  find  scratched  pebbles 
along  this  line,  and  in  nearly  all  the  region  to  the  north 
of  it,  as  well  as  some  few  points  to  the  south  of  it.  If 
we  search  below  the  soil,  in  these  countries,  we  often  find 
the  rocks  still  scratched  by  the  work  of  the  ice  armed  with 
these  bits  of  stone.  From  these  proofs  we  are  certain 
that  a  thick  sheet  of  ico  once  lay  over  all  this  country, 
and  moved  southwards,  scratching  pebbles  and  rocks  as 


12  PEBBLES,  SAND,  AND  CLAY. 

it  went.  All  through  this  region  these  glacial  pebbles 
are  very  plenty,  sometimes  forming  hills  a  hundred  or 
more  feet  in  height.  So  plentiful  are  these  rudely-shaped 
pebbles  in  these  northern  countries,  that  we  find  more  of 
them  in  the  streams  and  on  the  sea-shore  than  either 
streams  or  sea  can  make  for  themselves.  There  are  many 
times  as  many  pebbles  made  by  this  ice-mill  now,  on  the 
surface  of  North  America,  as  have  been  made  by  the 
streams  or  waves  and  rivers  combined.  Indeed,  a  large 
part  of  the  work  now  done  by  the  rivers  and  sea-shore 
waves  consists  in  shaping  out  and  rearranging  the  pebbles 
that  the  ice  has  left  over  the  land.  We  cannot  now  turn 
aside  to  consider  the  history  of  this  wonderful  ice  time,  for 
we  intend  to  go  only  as  far  as  the  pebbles  serve  to  show 
the  way ;  yet  we  see  that  these  bits  of  scratched  stone, 
when  we  read  them  aright,  open  to  us  a  wonderful  chapter 
in  the  earth's  history.  So  is  it  with  all  the  things  of 
this  world.  If  we  could  see  all  that  one  of  these  little  bits 
of  stone  has  lived  through,  we  should  be  able  to  look  back 
through  a  mighty  past,  that  would  startle  us  with  its 
strange  scenes. 


LESSON  IV. 
SAND. 

WHILE  looking  at  the  history  of  pebbles,  we  often  find 
ourselves  in  company  with  its  numerous  humbler  kinsmen, 
the  sand-grains.  At  first  sight  it  might  seem  that  these 
sand-grains  are  only  little  pebbles  that  are  near  the 
end  of  their  long  combat  with  the  water,  —  that  fight 
they  wage  so  well,  though  in  the  end  they  are  overcome : 


SAND.  13 

but,  when  we  look  closely  at  them,  we  see  that  although 
there  are  pebbles  no  bigger  than  large  grains  of  sand,  a 
grain  of  sand  is,  after  all,  a  different  thing  from  a  little 
pebble. 

If  we  take  some  sand  from  a  river,  —  where,  as  with 
pebbles,  we  will  begin  our  study  of  sand,  —  we  generally 
find,  if  we  look  closely, and  especially  if  we  take  a  common 
magnifying-glass  to  aid  us,  that  these  grains  are  sharp- 
angled,  with  flattened  sides,  and  that  they  are  generally 
like  bits  of  glass,  letting  the  light  through  them,  though 
not  exactly  transparent.  This  shows  us  that  sand-grains 
are  in  fact  crystals,  generally  of  a  substance  called  quartz. 
We  can  easily  satisfy  ourselves  that  these  grains  are  harder 
than  most  stones ;  by  rubbing  sand-grains  upon  the  stones, 
they  will  scratch  these  stones  without  breaking  the  sharp- 
ness of  the  edges  of  the  grains.  The  only  change  that 
comes  over  the  grains  is  that  many  of  them  break  into 
two  or  more  pieces,  which  still  preserve  the  sharpness  of 
the  larger  bits.  Even  the  powdery-looking  stuff,  if  we 
look  closely  at  it  with  a  microscope,  is  seen  to  be  made  up 
of  small,  sharp  bits. 

If  we  compare  the  sand-grains  with  a  tiny  pebble  of  the 
same  size,  using  a  strong  magnifying  power  to  aid  our 
sight,  we  find  that  the  grains  of  sand  are  all  composed  of 
one  like  substance,  while  the  pebble  is  made  up  of  many 
grains  of  different  sorts  of  substances.  This  substance  of 
most  sand  is  the  same  as  glass ;  indeed,  glass  is  made  by 
melting  sand,  using  some  potash,  soda,  or  lime  only  to  aid 
the  melting.  We  know  how  hard  and  cutting  bits  of 
glass  are ;  sand-grains  are  even  harder ;  for  it  is  necessary 
to  put  some  other  substance  into  glass  to  make  it  melt 
easily,  and  this  softens  it  somewhat. 

As  we  go  up-stream,  searching  for  the  place  where  the 


14  PEBBLES,   SAND,    AND   CLAY. 

sand  is  formed,  we  do  not  find  the  grains  growing  much 
larger,  however  far  we  have  to  go  to  find  the  place  vriiere 
it  is  made.  This  is  a  proof  that  the  sand-grains  do  not 
wear  so  fast  as  the  pebbles ;  for  the  lessening  in  the  size  of 
the  pebbles  as  we  go  down  stream  is  very  marked.  Often 
a  good  deal  of  the  sftnd  comes  from  the  pebbles  themselves; 
for  these  pebbles  are  often  composed  in  part  of  quartz 
crystals,  which  break  out  in  the  shape  of  sand-grains  when 
the  pebbles  are  pushed  along  the  bed  of  the  stream  and 
bruised  against  each  other.  But  when  a  stream  abounds 
in  sharp  sand,  we  shall  find  that  along  its  course  there  are 
some  rocks  composed  in  part  of  quartz,  such  as  granite, 
or  syenite,  or  sandstone.  When  these  rocks  decay,  they 
fall  to  pieces,  and  these  grains  of  sand,  being  lighter  than 
many  other  things  that  make  rocks,  are  easily  moved  by 
the  tiniest  rills  to  the  nearest  stream,  and  they  can  jour- 
ney down  to  the  sea  without  any  trouble.  In  all  rivers 
that  have  anything  to  make  sand  of,  along  their  banks, 
there  is  a  constant  stream  of  sand  moving  down  to  the  sea, 
—  more  in  times  of  flood  than  in  low  water,  but  always 
some.  In  the  Arno,  in  Italy,  on  the  banks  of  which 
these  pages  are  written,  we  have  a  good  instance  of  this. 
Where  the  stream  goes  through  Florence,  it  is  a  rather 
small  river,  indeed  less  than  the  Merrimac,  the  Mohawk, 
or  the  Great  Miami  rivers  of  America.  A  dam  across  the 
stream  deadens  the  current,  and  helps  the  sand  to  settle 
to  the  bottom.  Boatmen  with  long  scoops  are  constantly 
taking  out  this  sand  from  the  pool  below  the  dam,  many 
cartloads  a  day  being  thus  removed.  But  there  is  never 
any  lack  of  new  sand  to  fill  the  places ;  when  one  place  is 
cleared,  a  few  days  suffice  to  fill  it  up  again ;  yet  this  is 
not  what  would  be  called  a  very  sandy  river.  In  some 
parts  of  the  Allegheny  mountain  country,  where  all  the 


SAND   OF  THE   SEA-SHORE.  15 

rocks  are  sandy  and  decay  quite  rapidly,  the  streams 
carry  so  much  sand  that  it  is  not  possible  to  make  a  mill- 
pond  that  will  be  of  any  use,  for  the  basin  will  be  rilled  up 
in  a  few  months'  time. 

As  these  sand-grains  have  sharp  edges,  and  are  harder 
than  any  other  stones,  they  cut  the  stones  they  slip  over. 
Whenever  one  stone  is  driven  over  another,  there  are 
generally  some  grains  of  sand  below  the  rock  to  help  to 
wear  them  away.  The  cutting  power  of  a  stream  of 
water1  depends  very  much  on  the  amount  of  sand  or  peb- 
bles it  has  in  it.  If  we  drive  a  stream  of  pure  water 
against  a  pane  of  glass,  it  will  not  affect  it,  even  if  we 
keep  it  moving  at  a  high  speed  for  days ;  but,  if  we  have 
a  little  sand  on  it,  the  water  will  drive  the  sand  against 
the  glass,  and  in  a  few  minutes  it  will  appear  ^ike  ground 
glass,  from  the  cutting  action  of  the  sand.  In  the  same 
way,  the  river-water  gets  a  power  of  wearing  stones.  In  a 
similar  fashion,  the  sand  is  used  in  glass-cutting  to  shape 
figures  on  the  surface  of  the  glass.  If  the  workman  wishes 
to  make  a  figure  like  a  leaf,  he  pastes  a  paper  on  the  glass, 
leaving  the  figure  of  a  leaf  bare.  He  then  puts  the  glass 
in  a  blast  of  air,  or  steam,  that  drives  sand  at  a  high  speed 
against  it,  and  in  a  short  time  the  bare  part  is  cut  so  that 
it  appears  white,  while  the  paper  protects  the  rest  of  the 
surface  from  the  cutting  power  of  the  sand. 


LESSON  V. 

SAND  OF  THE   SEA-SHORE. 

NOWHERE  else  in  the  world  can  we  see  sand  to  so  much 
advantage  as  on  the  sea-shore.  Indeed,  most  shores  seem 
at  first  sight  like  only  sea  and  sand.  On  the  sea-shore  we 


16  PEBBLES,   SAND,   AND   CLAY. 

find  the  sand  is  the  best  friend  the  land  has  in  its  eternal 
combat  with  the  sea.  On  far  more  than  half  the  coasts  of 
the  world  it  forms  a  sort  of  armor,  on  which  the  pebble- 
armed  sea  can  strike  its  blows  without  such  destructive 
effects  as  it  would  bring  about  on  bare  rocks. 

If  we  examine  a  beach  when  the  surf  is  rolling  in  upon 
it,  we  may  see  how  the  sand  resists  the  mighty  blows  that 
are  struck  against  it.  When  the  wave  lifts  itself  into  a 
great  wall  to  tumble  on  to  the  beach,  the  hard  grains  of 
sand  lie  close  together  so  compacted  that  the  foot  will 
hardly  make  a  print  upon  them  ;  yet  between  the  grains 
is  a  little  cushion  of  water  which  keeps  them  from  wearing 
against  each  other.  When  the  blow  is  struck,  the  sand 
hardly  feels  the  effect ;  a  part  of  it  is  stirred,  but  the 
grains  are  so  wrapped  about  with  water  that  they  do  not 
harm  each  other.  If  they  were  pebbles,  they  would  pound 
against  each  other  with  a  roar  that  we  should  hear  above 
the  sound  of  the  waves ;  but  the  littleness  and  lightness 
of  the  sand  gives  it  security.  It  is  only  when  the  sand 
gets  between  stones,  that  are  pounded  together  by  the 
waves,  that  it  is  much  worn  ;  then  some  of  its  grains  are 
ground  to  fine  powder.  The  most  of  the  sand  we  find 
on  the  sea-shore  is  made  by  this  pounding  of  the  stones 
together.  In  this  pounding  both  stones  and  mud  wear 
very  rapidly,  some  part  of  each  being  ground  into  the  fine 
powder  we  call  "mud,"  a  form  of  bruised  stone  which  we 
have  soon  to  consider. 

Above  the  point  where  the  waves  beat  most  fiercely, 
where  the  broken  water  of  the  surf  writhes  hurriedly  about 
in  foaming  eddies,  the  sand  moves  far  more  than  when  it 
receives  the  solid  blow  of  the  falling  waves.  Here,  too,  it 
moves  but  little,  but  it  makes  a  mill  where  little  pebbles 
and  bits  of  shell,  sea-weed,  etc.,  are  cut  up  by  its  sharp 


SAND   OF   THE   SEA-SHORE.  17 

points,  and  gradually  ground  into  powder.  This  is  an 
important  work  for  the  sand  to  do,  as  it  makes  a  great 
deal  of  muddy  matter,  out  of  which  the  sea  builds  rocks, 
as  we  shall  see  hereafter.  It  also,  by  grinding  up  rubbish, 
keeps  the  sea-beach  the  clean,  orderly  place  we  always 
find  it  to  be. 

The  heavy  storms  throw  a  good  deal  of  sand  above  the 
level  attained  by  ordinary  waves.  This  becomes  very 
dry ;  few  plants  can  grow  upon  it,  and  these  are  killed  by 
the  next  heavy  storm.  When  the  tides  are  low,  the  hot 
sun  soon  dries  the  exposed  surface  of  sand  down  to  near 


Fig.  8.    Dunes  that  destroyed  Eccles,  Norfolk,  England. 

the  level  of  low  tide.  When  the  wind  blows  strongly  from 
the  sea,  it  moves  this  sand  before  it.  We  can  at  such  times 
see  little  streams  of  blown  sand  moving  up  the  beach  until 
they  are  beyond  the  reach  of  the  waves.  This  sand  helps 
to  make  the  high  beach  wall  that  often  lies  along  the 
shore.  On  most  shores  the  winds  from  the  land  side  soon 
blow  most  of  this  back  into  the  water.  But  if  it  happens 
that  the  winds  from  the  sea  are  more  powerful  than  those 
from  the  land,  this  sand  keeps  working  inland,  and  gathers 
into  great  heaps  called  "  dunes."  These  dunes  are  sometimes 
more  than  a  hundred  feet  high,  and  miles  in  length.  (Fig. 
8.)  The  sand  from  the  seaward  side  keeps  blowing  over 


!#  PEBBLES,  SAND,  AND  CLAY. 

to  the  landward  side,  and  so  the  dunes  slowly  wend  away 
from  the  sea-shore,  sometimes  marching  slowly  inland  and 
overwhelming  fields  and  villages  as  they  go.  On  the 
Atlantic  coast  of  North  America  the  winds  are  generally 
from  the  west,  hence  the  dunes  do  not  often  have  a 
chance  to  form,  for  the  sand  is  blown  out  to  sea.  But  in 
Europe,  the  same  west  winds  carry  the  sand  inland.  In 
the  head  of  the  Bay  of  Biscay  these  sand-heaps  are  of  very 
great  size,  and  have  covered  a  great  deal  of  land.  But 
for  certain  plants  which  flourish  even  on  the  sand,  and 
tend  to  bind  it  together,  it  would  not  be  possible  to  save 
many  fertile  regions  from  these  dunes;  but  the  grasses 
knit  them  together  in  a  firm  way,  so  that  the  wind  cannot 
move  them.  If  by  any  chance  a  hole  is  made  in  this 
covering  of  grass,  the  wind  getting  into  it  will  sometimes 
tear  the  hill  away.  Even  a  footstep  will  sometimes  start 
the  break  in  the  bonds  the  grass  puts  upon  it. 

On  the  land  side  the  wind  tends  to  take  the  sand  away 
from  the  shore ;  and  on  the  sea  side  the  currents  of  the 
water,  especially  of  the  tides,  work  to  pull  the  sand  out  to 
sea.  We  find,  by  drawing  up  specimens  of  the  bottom  in 
dredges,  that  the  sea-floor,  for  hundreds  of  miles  from  the 
land,  is  covered  by  sands  that  wander  to  and  fro  in  the 
sway  of  the  currents  that  sweep  near  the  shore.  These 
sands  have  all  been  formed  in  the  course  of  ages  along 
the  shores  or  in  the  rivers.  But  the  most  of  the  work  of 
making  sand  is  probably  done  on  the  surface  of  the  land 
by  the  decay  of  the  rocks,  which  fall  into  sand,  and  are 
then  carried  by  the  streams  into  the  sea ;  where,  because 
of  its  fineness  and  lightness,  it  may  easily  wander  very  far 
even  in  slight  currents. 

If  we  take  up  a  little  of  any  soil,  we  are  pretty  sure  to 
find  that  it  is  partly  composed  of  sand.  In  most  regions  this 


SAND   OF   THE   SEA-SHOKE. 


19 


sand  is  always  part  of  the  soil.  So  we  see  how  universal 
this  sort  of  matter  is  in  the  world.  If  by  any  change  of 
climate  a  soil  becomes  too  dry  for  plants  to  live,  as  in  the 
Sahara  Desert,  then  the  soil  becomes  the  prey  of  the 
winds,  that  sweep  it  about  and  make  great  dunes  of  mov- 
ing sand  and  finer  dust.  These,  as  well  as  the  sea-sands, 
may  blow  into  fertile  countries  and  reduce  them  to  deserts. 
In  this  way  the  African  deserts  are  always  trying  to  gain 


Fig.  9.    Nile  Delta  and  neighboring  Deserts. 

on  the  fertile  land  of  Egypt.  If  it  were  not  for  the  plants 
that  hold  the  soil  down,  so  that  the  wind  cannot  get  hold 
of  it,  all  our  earth's  surface  would  be  as  uneasy  as  the 
sands  of  the  Sahara. 

Sand  is  also  plentifully  formed  beneath  glaciers,  even 
more  plentifully  than  on  the  shores  or  in  the  streams,  for 
there  the  pressure  is  far  greater,  and  the  stones  are  easily 
crushed  by  it. 

When  the  sand  is  sharp,  and  blown  in  quantities  by  the 
wind,  it  sometimes  cuts  the  rocks  a  good  deal.  In  some 
parts  of  the  Rocky  Mountains  it  polishes  and  scratches  the 
stones  in  the  process.  On  some  shores,  when  the  wind 
blows  along  the  coast,  the  pebbles  are  slowly  worn  away 
by  the  sharp  grains  that  are  constantly  swept  over  them. 


20  PEBBLES,  SAXD,  AND  CLAY. 


LESSON  VI. 

MUD. 

As  the  sand  comes  below  the  pebbles  in  size,  so  these 
mud  grains,  which  we  are  about  to  study,  are  less  than 
the  sand.  Mud  grains  are  so  small  that  we  cannot  see 
them  well  without  the  microscope,  and  they  have  none  of 
the  charm  for  the  eye-  that  belongs  to  clean  pebbles  or 
sharp  sand ;  yet,  like  all  other  things  that  at  first  sight 
seem  to  want  beauty,  mud  is  full  of  interest  and  of  beauty, 
too,  when  we  come  to  understand  it. 

If  we  put  some  mud  under  the  microscope,  we  find 
that  it  is  composed  of  small  powdered  and  battered  grains 
of  rock,  many  kinds  commonly  being  mingled  together  in 
the  mass.  We  see  that  some  of  the  bits  are  like  little  peb- 
bles, being  composed  of  several  sorts  of  stone  in  the  same 
piece ;  others  are  very  small  fragments  of  sand  that  have 
become  decayed  and  softened  after  their  long  battle  with 
the  waters.  We  also  often  find  little  bits  of  plants,  frag- 
ments of  shells,  etc.  In  other  words,  mud  is  the  result  of 
the  constant  battering  that  serves  to  break  the  fragments 
of  rock  into  small  pieces,  and  of  the  decay  that  con- 
stantly divides  the  bits  into  yet  smaller  particles. 

If  we  put  a  little  of  this  mud  into  water,  we  see  that, 
unlike  sand  and  pebbles,  it  does  not  at  once  fall  to  the 
bottom  of  the  vessel,  but  remains  like  a  cloud,  only 
slowly  settling  to  the  bottom.  Some  of  it  will  go  down 
in  a  few  minutes,  some  will  fall  in  a  day,  but  even  in  a  bot- 
tle only  six  inches  high  there  will  be  some  that  will  require 
a  day  to  find  its  way  to  the  bottom. 

If  we  go  to  any  stream,  we  shall  find  that,  if  it  be  a 


MUD.  21 

mountain  brook,  there  will  be  but  little  mud,  and  that 
coarse  grained.  Stirring  the  water,  we  find  that  the  cloud 
of  mud  that  is  raised  quickly  falls  to  the  bottom,  showing 
that  it  is  coarse  grained.  This  is  because  the  finely  divided 
rock  easily  runs  away  in  the  swiftly  flowing  water,  and  is 
carried  off  as  fast  as  it  is  made.  Going  down  stream  to 
where  the  water  flows  more  slowly,  we  shall  find  the  mud 
becoming  finer  and  finer,  as  is  shown  by  the  fact  that,  if 
we  stir  the  bottom,  the  water  will  remain  muddy  for  a 
longer  time.  As  we  go  towards  the  mouth  of  a  large 
river,  such  as  the  Mississippi,  we  find  the  water,  though  it 
moves  slowly,  is  always  clouded  with  mud,  and  the  banks 
are,  in  the  main,  made  of  mud  of  the  finest  sort.  Such  a 
stream  is  always  rolling  out  to"  sea  a  great  mass  of  this 
mud,  so  finely  divided  that  it  may  stay  afloat  for  weeks 
and  months,  and  thus  be  carried  to  distant  parts  of  the 
sea. 

This  finely  divided  rock  which  we  see  as  mud  is  abun- 
dantly formed  on  the  sea-shores,  as  well  as  in  the  streams. 
The  stones  grinding  together  wear  into  this  shape,  and  the 
sand  that  is  rubbed  between  them  has  the  same  fate.  We 
see  little  of  the  mud  on  the  shore,  because  the  currents 
formed  by  the  tides  and  winds  easily  bear  it  out  to  sea ; 
but,  at  very  low  tide,  we  often  see  very  broad  flats  made 
entirely  of  mud ;  and,  if  we  look  in  the  bays  along  the 
shore,  we  often  find  that  thousands  of  acres  of  land  have 
been  built  by  the  mud  that  has  been  drifted  in  from  the 
sea  by  the  tidal  currents,  and  caught  by  the  salt-water 
plants.  Yet  more  of  this  mud  from  the  shore  goes  far  off 
to  sea,  and  falls  on  to  the  deep  ocean  floors. 

Yet  the  most  of  the  mud  is  not  ground  up  by  the  sea- 
waves,  or  the  rubbing  of  stones  on  the  river-bed.  It  is 
made  in  and  beneath  the  soil,  by  the  action  of  decay, 


22  PEBBLES,  SAND,  AND  CLAY. 

brought  about  by  water,  and  also  by  the  work  of  plants 
and  animals.  If  we  take  some  soil  from  a  field,  and  dis- 
solve it  in  water,  we  find  that  it  is  partly  composed  of  sand, 
in  part  of  decayed  plants,  but  in  yet  larger  part  of  grains 
of  mud.  These  mud  grains  generally  make  up  more  than 
half  the  whole.  In  all  fertile  soils  they  are  much  more 
than  half  the  total  mass.  If  we  look  closely,  we  may 
see  what  are  the  means  whereby  these  mud  grains  are 
made. 

When  water  goes  through  the  layer  of  decaying  plants, 
it  takes  up  certain  acids  from  it.  These  acids  are  formed 
by  the  decay  of  the  dead  plants  in  the  soil.  By  these 
acids,  as  well  as  by  the  oxygen,  which  in  part  composes 
it,  water  has  a  very  great  power  of  rotting  the  rocks  into 
fine  powder.  This  process  is  called  oxidizing.  A  famil- 
iar instance  of  it  is  seen  when  iron  rusts  in  the  ground, 
When  the  ground  freezes  and  thaws,  this  dividing  of  the 
stones  is  greatly  helped ;  for,  the  water  soaking  into  them, 
and  then  swelling  when  it  turns  into  ice,  bursts  them  into 
dust.  Then  a  singular  work  is  done  by  the  earth-worms. 
These  creatures  get  their  living  by  eating  their  way 
through  the  soil.  They  take  the  earth  into  their  stom- 
achs, take  from  it  what  there  may  be  that  they  can  digest ; 
they  then  cast  the  earth  out  again;  but,  while  in  their 
bodies,  the  earth  is  exposed  to  the  acids  which  serve  to 
digest  the  food,  and  is  more  finely  divided.  Now,  as  in 
most  soils  there  are  many  thousands  of  these  worms  to 
the  acre,  and  as  they  are  always  at  work,  except  when  the 
ground  is  frozen,  it  is  reckoned  that  they  pass  all  the 
soil  on  which  they  live  through  their  bodies  every  few 
years.  There  is  no  doubt  that  these  humble  creatures  do 
a  work  that  is  fit  to  be  compared  with  that  of  the  rivers  or 
sea-shores,  in  grinding  up  the  elements  of  the  earth  into 
the  finest  mud. 


MTTD.  23 

In  this  work  of  dividing  the  fine  grains  of  the  soil  the 
roots  of  plants  also  take  an  important  share.  The  little 
fibrils  that  the  roots  put  out  are  very  slender,  —  sometimes 
so  small  that  the  eye  can  just  perceive  them.  These,  en- 
tering into  the  crevices  of  the  mud  grains,  grow  larger, 
and,  as  they  expand,  burst  them  apart.  The  roots  of  the 
larger  plants,  as  they  grow  larger,  exert  an  immense  force. 
They  may  pry  rocks  apart  as  if  they  were  wedges  of  steel. 
We  see  a  little  of  their  power  on  the  streets,  when  they 
sometimes  lift  the  paving  stones.  The  first  little  thread 
of  the  root  is  so  slender  that  it  can  insert  itself  into  the 
crevices  that  lie  between  the  grains  of  sand  and  mud ;  and, 
once  there,  it  can  soon  gather  power  to  rend  them. 

The  largest  share  of  the  mud  we  find  in  a  river  is  not 
made  in  its  bed,  but  is  carried  from  the  land  by  the  rains, 
which  very  easily  dissolve  it  and  convey  it  away.  We  have 
only  to  watch  a  plowed  field  to  see  how  large  the  amount 
is  that  goes  away  with  every  rain.  Were  it  not  that  the 
forces  that  break  up  the  rocks  into  this  mud  are  always 
at  work,  there  would  soon  be  no  place  for  the  plants  to 
grow,  so  fast  do  the  streams  carry  it  away. 

We  have  now  seen  in  part  how  the  machinery  of  the 
waters,  aided  by  other  forces,  such  as  frost,  roots,  and  the 
stomachs  of  worms,  serve  to  divide  up  the  rocks  of  the 
earth  into  very  tiny  bits,  that  can  be  easily  carried  by 
water.  When  in  this  divided  state,  a  good  part  of  the 
matter  tarries  on  the  land,  and  helps  make  our  soils;  the 
rest  goes  to  the  sea,  and  helps  make  the  rocks  that  are 
constantly  forming  there. 

We  will  now  turn  aside  to  consider  the  history  of  soils, 
for  on  them  depends  all  the  usefulness  of  the  world  to 
man.  Then,  afterwards,  we  will  see  what  becomes  of  the 
mud  and  sand  that  goes  from  the  rivers  and  shores  to  the 
Depths  of  the  seas. 


24  PEBBLES,   SAND,   AND  CLAY. 

LESSON  VII. 

SOILS. 

THE  most  important  result  of  this  battle,  that  is  waged 
against  the  rocks  by  the  air,  rain,  etc.,  is  the  chance  it 
gives  for  life  to  find  a  place  on  earth.  All  the  vegetable 
life  of  the  land  depends  upon  the  existence  of  soils,  and 
all  the  animal  life  would  have  no  chance  to  exist,  if  it 
were  not  for  the  plants.  Indeed,  much,  if  not  the  most 
of  the  life  of  the  sea,  as  we  shall  find  further  on,  is  fed  by 
the  things  the  soils  produce. 

In  any  field  we  have  one  of  the  common  shapes  which 
this  layer  of  earth  takes  on  the  earth's  surface.  If  we  look 
at  it  closely,  we  see  that  there  is  on  the  top  a  layer  of  a 
very  dark  color,  which  we  at  once  know  has  its  color  given 
to  it  by  the  decayed  plants  it  contains.  These  plants  turn 
black  as  they  rot;  and,  though  they  break  up  into  small 
bits,  we  can  still  see  on  the  surface  that  they  are  bits  of 
plants.  This  is  plain,  for  the  plants  are  not  altogether 
decayed,  and  keep  their  shape.  As  we  go  downward,  these 
bits  of  dead  plants  gradually  pass  into  a  brownish  mould. 
As  we  dig  yet  deeper,  this  disappears,  and  we  have  the 
earth  without  any  mixture  of  plant-fragments,  but  only 
colored  by  the  stain  of  decayed  plants.  As  we  go  yet  fur- 
ther down,  the  soil  becomes  harder,  until  we  come  to  the 
rock.  This  rock  is  generally  soft  at  the  top,  and  broken  up 
by  the  roots  that  work  into  it.  Below  tliis  level  it  is  found 
to  be  quite  solid. 

This  is  the  common  sort  of  soil  over  all  the  world,  ex- 
cept on  certain  regions,  of  which  we  shall  speak  presently. 
Such  a  soil  is  made  by  the  gradual  decay  of  the  rock.  If 


SOILS.  .          25 

we  should  strip  it  all  away  down  to  the  solid  rock,  it  would 
begin  to  form  again  in  the  following  way :  After  a  few 
years'  exposure  to  the  air,  the  stone  would  decay  a  little, 
and  the  seeds  of  lichens  falling  upon  it  would  find  a  little 
softened  rock  to  fix  themselves  upon.  These  simple 
plants  need  no  soil,  for  they  have  no  roots ;  they  only 
need  a  roughened  stone  to  fix  themselves  upon.  They 
soon  make  a  close  net  over  the  surface,  so  that  it  is  quite 
hidden  from  sight.  They  keep  the  surface  moist,  and  the 
acids  made  in  the  water  by  their  decay  help  to  rot  the 
stone.  Soon  there  is  a  little  earth  gathered  in  the  small 
hollows  of  the  rock ;  and,  in  these,  grasses  and  low  shrubs 
find  a  foothold.  These,  with  their  roots,  help  to  break  up 
the  decaying  stones,  so  that  they  may  rot  the  faster.  It 
takes  many  years,  perhaps  centuries,  to  get  this  beginning. 
These  larger  plants,  when  they  die,  make  a  mould  that 
grows  thicker  and  thicker  as  time  goes  on,  so  that  it  comes 
to  be  fit  for  the  roots  of  trees.  The  seeds  of  pines,  poplars, 
willows,  and  other  trees  with  seeds  so  small  that  they  need 
little  covering,  and  so  light  that  they  can  be  carried  by 
the  wind,  are  constantly  trying  to  find  places  to  grow;  and, 
as  fast  as  this  soil  grows  thick  enough  for  their  use,  they 
spring  up  upon  it.  Soon  we  have  the  beginning  of  a  for- 
est, which  is  at  first  very  stunted,  because  the  soil  is  so 
thin.  But  this  soil  now  grows  rapidly  in  two  ways :  first, 
by  the  decay  of  the  leaves  of  the  trees,  as  well  as  by  their 
trunks  and  branches  when  they  die  ;  and,  secondly,  by  the 
action  of  the  roots,  as  well  as  of  the  frosts,  in  breaking  up 
the  stones  at  the  bottom,  so  that  they  may  rot  the  faster. 
The  breaking  up  of  the  stones  helps  the  rotting  by  add- 
ing  to  the  surface  over  which  decay  goes  on.  If  we  have 
a  solid  mass  of  rock  like  a  floor,  it  rots  only  over  its  sur- 
face ;  if  it  breaks  up  into  bits,  the  surface  over  which  the 


26  PEBBLES,    SAND,   AND   CLAY. 

decay  goes  on  may  be  ten  or  twenty  times  as  large,  and 
the  decaying  equally  increased  in  rate. 

All  the  while  the  rock  is  breaking  up  into  bits  in  this 
fashion,  the  rain-water  is  washing  through  it,  becoming 
soaked  full  of  acids  as  it  passes  through  the  decaying 
bed  of  leaves,  and  with  them  dissolving  the  rock  into  its 
waters.  In  this  shape  the  substances  of  the  soil  are  ready 
to  be  taken  into  the  plant  through  its  tender  roots.  If  the 
plants  are  numerous,  and  the  water  goes  slowly  through 
the  soil,  a  good  deal  of  this  stuff  the  water  takes  into 
solution  is  caught  up  by  the  plants  into  their  bodies,  and 
for  a  while  rests  above  the  soil  in  the  light  of  the  sun. 
By  and  by  it  falls  by  death,  decays,  and  the  ceaselessly 
acting  water  has  another  chance  to  drag  it  down  with  it 
to  the  sea.  All  the  water  that  runs  from  the  ground  in 
springs  takes  some  part  of  this  plant-food  with  it  which  the 
soil  never  recovers ;  but,  while  it  robs  the  soil  of  a  part  of 
its  richness,  it  gives  more  than  it  takes,  by  its  effect  in 
helping  the  decay  of  the  rocks. 

The  richness  of  soil  depends  upon  two  things:  first 
and  foremost,  on  the  nature  of  the  rock  below  it,  that  is 
to  say,  on  the  kind  of  substances  that  the  rock  has  in  it. 
If  the  rock  be  a  limestone  with  a  great  many  fossils,  it  is 
sure  to  do  its  part  of  the  soil-making  in  a  perfect  way, 
and  give  a  fertile  earth.  Next,  the  soil  depends  on  the 
action  of  the  plants  which  yield  it  the  vegetable  matter, 
without  which  the  rocks  alone  could  not  make  the  soil 
rich,  for  it  is  the  acids  that  the  water  gains  from  the  de- 
caying plants  that  enable  it  to  dissolve  a  sufficient  part 
of  the  materials,  so  that  the  plants  can  get  a  hold  on 
them.  Of  all  the  mass  of  a  soil,  probably  not  more  than 
the  thousandth  part  is  at  any  one  moment  ready  for  plant- 
food.  The  greater  part  stays  undissolved,  and  it  only 
slowly  goes  into  the  shape  of  food  for  the  plants. 


SOILS.  27 

Let  us  see  now  what  is  done  when  man  comes  to  use 
the  soil  for  the  crops  on  which  depend  all  his  arts.  The 
rudest  savage  ranges  through  the  forest,  and  takes  only 
its  fruits  and  its  wild  animals;  but  such  peoples  are  rare. 
Almost  every  tribe  in  the  world  gets  some  profit  out  of 
the  soil  by  tillage.  This  can  only  be  done  by  stripping 
away  the  natural  plants,  and  using  their  place  for  those 
which  suit  man's  needs.  On  the  perfection  of  his  meth- 
ods in  this  work  depends  all  his  chances  of  civilization 
and  wealth;  for,  however  much  wealth  and  culture  are  at 
times  separated  from  agriculture,  they  always  have  their 
roots  in  this  art,  even  as  the  trees,  however  high,  depend 
on  the  earth  beneath.  When  he  tills  the  soil,  man  de- 
stroys its  old  natural  state,  and  makes  all  its  processes 
somewhat  unnatural.  When  the  plants  are  stripped  away 
the  rain  no  longer  does  the  same  work  of  creation  alone, 
but  it  becomes  a  destroyer.  The  sponge-like  mass  of 
dead  leaves,  twigs,  and  trunks  that  make  up  a  forest  bed, 
holds  the  running  water  away  from  the  soil,  until  it  gets 
into  considerable  streams.  These  generally  cut  down 
into  the  rock,  and  so  harm  the  soil  but  little  ;  they  eat 
only  a  little  away  along  the  river-banks.  When  the  soil 
is  tilled,  the  rain  strikes  on  the  surface  of  the  bare  earth, 
and  sweeps  great  quantities  into  the  streams.  If  the  hills 
be  steep,  we  often  see  the  whole  soil  upon  them  carried 
away,  leaving  the  bare  rock,  thus  destroying  in  a  few 
years  the  slow  work  of  ages.  When  the  soil  is  upturned 
by  the  plow,  it  is  left  very  open,  so  that  the  process  of 
decay  goes  on  rapidly,  and  it  is  possible  for  a  great  deal 
of  the  soil  to  come  into  the  shape  for  plant-food ;  but  the 
rain  is  the  more  able  to  bear  it  away,  and  so  the  soil  loses 
many  things  that  are  necessary  for  plants.  Now  the  crops 
take  away  much  of  the  rarer  kinds  of  substances  that  are 


28  PEBBLES,    SAND,   AND   CLAY. 

necessary  for  plant-life.  While  soils  are  always  gaining 
in  depth  and  fertility,  when  in  their  natural  crop  of  grass 
or  forests,  they  are  always  becoming  Isss  deep  and  less 
fertile  under  ordinary  tillage.  The  result  is  that  a  great 
deal  of  the  soil  of  the  earth  that  once  was  very  fertile  has 
been  ruined  by  the  plow.  A  skilful  agriculture,  that 
takes  pains  that  the  rains  do  not  wash  the  soils  away,  nor 
the  crops  take  away  more  than  the  natural  work  of  decay 
puts  into  a  state  for  plant-food,  may  be  maintained  with 
little  loss  of  the  earth's  fertility  for  thousands  of  years. 
In  England,  France,  and  Belgium,  where  the  soils  have 
been  carefully  husbanded,  they  yield  as  much  to  the  acre 
as  they  did  a  thousand  years  ago  or  more  ;  but,  in  Amer- 
ica, the  tillage  is  generally  very  careless,  because  soils  are 
cheap,  and  a  great  deal  of  the  land  is  ruined,  to  the  perma- 
nent loss  of  all  the  world  in  this  and  in  ages  yet  to  come. 

It  is  worth  while  to  look  closely  to  this  matter  of  soils, 
for  on  them  depends  the  future  of  all  countries  and  the 
life  of  man. 

While  the  process  of  soil-making  which  we  have  de- 
scribed is  the  method  that  is  followed  wherever  the  soil  is 
constructed  on  solid  rock,  there  are  other  and  rarer  methods 
followed  in  particular  parts  of  the  earth.  Along  the  river 
valleys,  for  instance,  there  is  a  strip  of  what  is  called 
alluvial  land,  which  has  been  made  by  the  earth  brought 
down  by  the  stream.  This  consists  of  a  very  deep  mass 
of  finely  divided  sand,  pebbles,  and  mud,  and  in  it  the 
plants  have  no  hard  task  of  breaking  up  the  rock,  nor  do 
they  have  to  wait  for  the  work  of  the  frost,  or  other 
decay ;  for  the  amount  of  finely  divided  matter  is  so  great, 
and  the  layer  so  deep,  that  the  plants  never  get  to  the 
bottom  of  it.  Indeed,  this  matter  of  the  alluvial  lands  is, 
for  the  most  part,  the  soil  that  has  been  washed  away 


SOILS.  29 

from  regions  further  up  the  stream,  and  left  here  because 
the  river  had  more  to  carry  than  it  could  manage  to  bear 
along.  Such  soils  are  almost  inexhaustible.  Then,  in  the 
regions  where  the  ice  of  the  glacial  sheet  has  acted,  there 
are  large  tracts  that  are  covered  by  a  great  thickness  of 
sand  and  gravel,  so  that  the  plants  never  get  access  to  th^ 
bed  rock,  and  have  not  to  wait  long  for  the  decay  to  form 
the  materials  out  of  which  to  make  a  soil.  These  soils  are 
generally  less  fertile  than  the  other  lands;  but,  because 
of  the  great  depth  of  the  substances  of  which  they  are 
made,  they  rarely  become  less  fertile  than  they  were  at 
first.  Thus,  the  New  England  soils  cannot  be  worn  out  as 
those  of  South  America  or  Virginia,  although  in  the  first 
place  they  were  not  so  rich. 

We  may  gather  up  this  account  of  soils  in  the  follow- 
ing words :  Soils  are  the  wreckage  of  the  rocks,  as  they 
wear  down  under  the  action  of  air,  rain  and  frost,  the 
roots  of  plants,  and  the  stomachs  of  earth-worms.  This 
wearing  has  been  going  on  for  a  very  long  time  in  the 
past,  so  that  the  soil  now  on  any  country  may  have  grad- 
ually settled  downwards  for  thousands  of  feet,  as  the 
rocks  slowly  rotted  away  and  were>  carried  off  by  the 
streams.  It  is  a  beautiful  fact  that  the  greatest  work  of 
ruin  that  the  world  knows  — •  the  decay  of  the  continents 
themselves — should  give  us  the  foundations  on  Avhich  to 
rest  all  the  higher  life  of  the  world.  All  our  forests  and 
prairies  owe  their  life  to  this  decay.  All  the  higher  ani- 
mals of  the  world  depend  upon  this  plant-life,  and  man 
himself  founds  his  life  upon  the  same  mass  of  ruin.  Thus 
it  is  through  all  the  life  of  the  world:  the  death  of  one 
thing  gives  life  to  others ;  the  decay  of  the  physical  world 
is  the  foundation  for  the  higher  life  of  plant  and  animal. 


CHAPTER    II. 


THE  MAKING   OF  ROCKS. 


LESSON  I. 
CONGLOMERATE. 

TDEBBLES  have  been  studied  in  the  first  lesson,  but 
-*-  we  stopped  our  study  with  the  loose  pebble,  as  it 
lay  011  the  river-bottom,  the  sea-shore,  or  where  the  glacier 
left  it.  But,  as  we  can  see  from  any  specimen,  pebbles 
may  take  on  other  shapes.  They  may  be  bound  together 
so  as  to  form  rocks  of  a  very  solid  sort,  which  are  termed 
conglomerates  or  pudding-stones,  so  called  because  of  the 
plum-like  look  of  the  pebbles  in  the  mass.  There  are 
some  beds  of  rock  in  the  earth's  crust,  of  very  great  ex- 
tent, that  are  full  of  these  pebbles.  One  of  .these  sets  of 
rocks  is  known  as  the  millstone  grit,  because  it  is  often 
used  for  making  the  stones  with  which  grain  is  ground. 
These  millstone  grits  lie  under  the  great  coal-beds,  whence 
comes  the  most  of  the  coal  used  in  the  world.  There  are 
many  other  great  sets  of  rocks  made  of  the  same  sort  of 
pebbly  beds.  Indeed,  it  seems  that  there  are  pebble-making 
times  in  the  earth's  history,  when  these  bits  of  rock  are 
made  in  such  quantities  that  it  is  hard  to  account  for  their 
production.  It  is  now  believed  that  these  pebbly  ages  are 
the  times  when  glaciers  are  peculiarly  abundant  on  the 
earth,  for  there  is  no  other  machinery  that  is  so  well  fitted 
to  make  them.  It  is  evident  that  the  conglomerates  are 


CONGLOMEEATE.  81 

mostly  made  in  salt  water ;  and  the  only  way  in  which 
such  vast  masses  of  pebbles  can  get  into  salt  water,  is 
through  the  action  of  glaciers.  The  great  rivers  do  not 
send  pebbles  into  the  sea.  None  much  larger  than  sand 
find  their  way  out  of  the  Mississippi  River  into  the  Gulf 
of  Mexico.  The  sea-shores  grind  up  about  all  that  they 
receive,  so  that  we  cannot  look  to  them  for  the  making  of 
the  great  conglomerate  beds. 

We  see,  from  specimens  of  conglomerate,  that  the  peb- 
bles are  bound  together  by  a  sort  of  cement  which  gener- 
ally consists  of  sand  and  clay, 
the  whole  forming  a  very 
hard  mass.  If  we  take  com- 
mon pebbles,  sand,  and  clay, 
and  mingle  them  together,  we 
do  not  have  this  solid  mass. 
How,  then,  could  this  mix- 
ture have  become  thus  hard  ? 
This  hardness  of  stones  made 

OUt    Of  bits   that  were   not   at  ^  10"    Conglomerate. 

first  bound  together  is  explained  in  part  by  the  pressure 
that  is  put  upon  them  when  they  are  buried  in  the  earth. 
These  rocks  were  once  deeply  buried  beneath  a  great 
thickness  of  other  rocks,  that  have  since  been  worn  away 
by  the  action  of  the  frost,  rivers,  and  the  sea-waves. 
For  a  long  time  thousands  of  feet  of  beds  lay  on  top 
of  these  compacted  rocks,  squeezing  their  mass  more 
powerfully  than  we  can  do  it  by  any  machinery.  We 
see,  in  the  making  of  brick  or  artificial  stone,  that  press- 
ure will  very  much  harden  the  mass.  Then  the  rocks 
have  generally  been  heated.  This  heating  took  place 
in  this  way:  The  depths  of  the  earth  are  very  hot.  We 
find  in  mines  and  deep  wells  that  the  heat  grows  one 


32 


THE  MAKING   OF    ROCKS. 


degree  higher  for  about  each  sixty  feet  of  depth;  so  that, 
if  these  rocks  are  buried  under  twenty  thousand  feet, 
or  about  four  miles  of  rocks,  they  will  lie  in  a  tempera- 
ture of  about  300°  Fahrenheit,  or  88°  above  boiling  water. 
Some  of  these  pudding-stones  have  had  a  yet  higher  tem- 
perature. We  see  in  brick-burning  how  the  heat  binds 
the  mass  of  soft  clay  together.  Then,  in  the  making  of 
artificial  stones,  it  is  the  custom  to  use  a  certain  amount 
of  either  silicate  of  potash,  called  soluble  glass,  or  silicate 
of  magnesia,  which  hardens  like  cement,  and  so  binds  the 
stuff  together.  This  is  imitated  from  the  processes  of  the 
earth,  for  it  is  just  the  way  in  which  the  rocks  are  often 
hardened. 


Fit/.  11.    Pebbles  aud  shell  elongated  by  pressure  (dotted  lines  show  original 


Sometimes  we  find,  in  the  way  the  stones  behave,  proof 
that  the  rocks  have  had  great  heat  and  pressure.  They 
often  stretch  out  until,  from  their  original  egg-shape,  they 
become  like  ribbons.  At  other  times,  the  pebbles  of  the 
hardest  rocks  have  been  pushed  into  each  other.  When 
these  pudding-stones  wear  away,  the  pebbles  fall  out,  and 
are  buried  in  other  deposits,  so  that  the  same  pebbles 
sometimes  find  their  way  out  of  one  bed  of  rocks  and 
into  another  of  a  later  age,  until  at  length  they  are 
destroyed  by  the  grinding  on  some  sea-beach,  or  worn 


CONGLOMERATE.  33 

out  in  their  long  journey  down  some  river,  or  else  they 
rot  to  pieces. 

As  a  pebble  grows  smaller  it  gets  better  able  to  stand 
the  wear  and  tear  that  the  world  gives  to  it.  A  large 
pebble  strikes  hard  blows  when  it  is  swung  by  the  sea  or 
rolled  by  a  river,  and  so  wears  rapidly;  but  the  little  ones 
are  less  heavily  beaten.  Besides,  it  is  always  the  very 
hardest  part  of  a  pebble  that  wears  to  the  end,  so  the 
small  bits  are  the  best  fitted  to  wear.  The  smaller  a 
thing  is  in  the  battle  with  the  waters  of  the  earth,  the 
safer  it  is  in  the  fight ;  for,  as  we  have  seen,  sand  wears 
very  slowly,  on  account  of  the  small  size  of  its  grains. 


34  THE  MAKING   OF    BOCKS. 

LESSON  II. 

SANDSTONES. 

WE  have  seen  the  sands  of  the  sea  and  of  the  rivers  in 
constant  motion  ;  we  have  now  to  notice  them  in  the  state 
of  repose,  in  which  they  are  when  built  into  solid  rocks. 
In  this  shape  they  make  up  a  large  part  of  the  visible 
crust  of  the  earth.  Sandstones  are  more  plentiful  than 
any  other  rocks  on  the  land,  as  sand  seems  more  plentiful 
on  the  rivers  and  along  the  sea-shore  than  any  other  sub- 
stance. Sometimes  these  sandstones  are  in  the  shape  of 
very  soft  rocks,  the  grains  hardly  holding  together.  Again, 
they  are  very  firmly  bound 
to  each  other,  and  at  times 
the  divisions  between  the 
grains  are  hardly  visible,  the 
whole  then  forming  a  very 
solid  mass. 

When  these  sandstones  are 
looked  upon  closely,  we  see 
that  they  always  show  a  cer- 

Fig.  12.    Sandstone.  ,    .  J.       £     '    ,,. 

tain   sort   01   bedding,  as  is 

indicated  in  the  figure.  These  are  the  great  .distinct  strata, 
as  we  may  find  in  the  limestones  and  clay-stones;  but,  be- 
sides these,  we  have  also  in  the  sandstones  what  is  called 
"  cross  bedding."  This  is  shown  in  Fig.  13.  We  see, 
besides  the  large  separate  beds,  that  there  are  sloping 
divisions  that  run  across  them.  If  we  would  understand 
how  this  works,  we  should  watch  the  sand  running  in  a 
sandy  gutter  of  a  rainy  day.  We  shall  see  that  the  bed 
of  sand  builds  out  at  the  end  in  sloping  banks. 


SANDSTONES. 


35 


The  arrow  shows  the  direction  of  the  current,  and  the 
letters  a,  i,  £,  e?,  e,  the  successive  layers  put  on  one  after  the 
other.  If  we  should  find  a  bed  below,  that  had  the  cross 
lines  sloping  the  other  way,  we  should  be  sure  that  when 
it  was  formed  the  stream  ran  contrary  to  the  course  of 
the  one  that  is  forming.  In  this  way,  in  sandstones  even 
of  the  oldest  day,  we  are  able  to  tell  which  way  the  cur- 
rents ran  that  brought  the  sands  to  their  place. 

These  old  sandstones  supply  a  large  part  of  the  sand 
that  we  find  in  the  rivers  and  on  the  sea-shore.  The  rocks 


Fig.  13.    Cross-bedded  Sandstone. 

decay  under  the  soil,  along  the  rivers  and  on  the  sea-shore ; 
but  the  grains  that  compose  them  live  on  and  take  shape 
again  in  rocks,  there  to  rest  for  ages;  but  again  to  be 
swept  out  by  the  water,  and  brought  once  more  into  the 
active  world. 

Sandstones  are  found  over  so  wide  a  surface  of  the 
world  because  sands  are  so  easily  carried  by  the  waters. 
Conglomerates  are  always  in  rather  narrow  strips,  because 
they  are  generally  formed  along  the  shore  lines,  the  cur- 
rents not  being  able  -to  carry  the  pebbles  that  compose 
them  far  to  sea. 


36  THE  MAKING  OF    BOCKS. 

LESSON  III. 

MUD    STONES. 

WE  have  seen  that  pebbles  and  sand  both  exist  on  the 
earth  in  two  shapes  :  in  one  they  are  moving  in  the  rivers 
and  on  the  sea-shore  in  constant  unrest  and  decay  ;  in  the 
other  they  are  motionless  in  the  rocks,  scarcely  changing 
in  millions  of  years.  Water,  which,  by  its  motion,  forms 
pebbles  and  sand,  serves  also  to  take  them  from  this  state 
of  rest,  and  return  them  to  the  state  of  activity.  The  same 
thing  occurs  with  the  finest  state  of  rocks,called  mud.  Mud 
is  buried  in  beds  firmly  bound  together,  and  after  a  time  is 
lifted  into  the  continents  and  mountains,  to  be  called  from 
its  resting-places  by  the  streams  and  frosts,  or  by  the 
decay  that  takes  place  beneath  the  soil.  The  clay-stones 
are  found  over  a  wider  field  than  either  the  sandy  or 
pebbly  rocks,  for  the  reason  that  the  currents  of  the  sea 
can  carry  this  fine  sediment  much  further  than  it  can 
sand,  as  they  can  carry  sand  very  much  further  than  they 
can  carry  pebbles.  When  the  sand  goes  out  of  rivers  or 
drifts  off  from  the  sea-shores,  it  cannot  travel  far  before  it 
must  come  to  rest  on  the  bottom  of  the  sea.  But  this 
mud  can  go  much  further.  Indeed,  some  of  it  is  constantly 
dropping  over  all  the  sea-floors.  The  volcanoes  which 
are  so  plentiful  along  the  shores  and  on  the  islands  of  the 
oceans  throw  out  a  great  deal  of  dust,  which  is  sometimes 
so  light  that  it  will  float  thousands  of  miles  through  the 
air  before  it  falls  to  the  ground  or  sea.  In  the  sea-water 
it  will  fall  even  more  slowly  than  in  the  air.  It  may  be 
months  in  getting  to  the  bottom ;  and,  as  the  sea-water  is 
always  moving,  it  may  be  carried  thousands  of  miles  away 


MUD   STONES. 


37 


from  the  place  where  it  alights  on  the  surface,  before  it 
finds  a  resting-place.  These  volcanoes  also  give  out  a 
great  deal  of  what  is  called  pumice.  This  is  stone  which, 
when  it  was  melted,  became  so  full  of  air-bubbles  that  it 
would  float  like  cork.  This  pumice  cannot  get  to  the 
bottom  until  it  rots,  which  may  require  tens  of  years.  It 
does  not  fall  all  at  once  to  the  bottom,  but  the  surface 
decays,  and  falls  off  in  fine  grains  that  slowly  sink  to  the 
sea-floor.  Only  when  it  is  much  decayed  will  it  sink  to  the 
bottom.  Thus,  those  parts  of  the  sea-floor  that  are  far  from 
land  have  a  little  mud  con- 
stantly coming  down  upon 
them.  These  mud  deposits 
form  very  slowly  ;  an  inch 
may  take  many  years  to 
build;  so  that,  when  we  see 
a  bed  of  fine-grained  clay- 
stone,  we  may  generally  be 


*"*/• 


Rate  of  Deposition. 


sure  that  the  time  taken  in  its  building  must  have  been 
much  greater  than  if  it  had  been  made  of  sand,  and  a  bed 
of  sand  or  lime  requires  more  time  than  one  of  pebbles  in 
its  making.  These  beds  of  clay  slate,  not  thicker  than 
roofing  slate,  may  have  required  many  years,  perhaps  a 
century,  in  their  formation.  This  may  give  a  measure  of 
geological  time.  When  we  remember  that  there  are  many 
sheets  of  clay  slate  that  are  thousands  of  feet  thick,  we 
may  conceive  how  long  it  took  them  to  be  built  in  the  old 
sea-floors  where  they  were  formed. 


muss 


38  THE  MAKING   OF    ROCKS. 

LESSON  IV. 

,     LIMESTONE. 

So  far  we  have  only  noticed  the  ways  by  which  certain 
rocks  were  made  by  the  action  of  water,  frost,  waves,  and 
other  causes,  upon  the  rocks  that  form  the  land.  We 
have  seen  that  through  the  work  of  the  water  a  certain 
part  of  these  rocks  is  constantly  passing  into  the  state  of 
sand,  pebbles,  or  mud,  and  then,  after  a  journey  in  the 
keeping  of  this  water,  falls  to  the  sea-floor  or  to  the  bottom 
of  lakes,  to  be  built  into  rocks  again. 

There  is  another  sort  of  rocks  we  must  now  study,  that 
differs  very  widely  from  those  before  described.  These 
are  the  limestones,  or  rocks  containing  lime,  that  abound 
in  every  part  of  the  earth.  The  rivers  and  the  sea-shores, 
that  show  us  the  ways  in  which  the  other  rocks  are  made, 
give  us  little  clew  to  the  origin  of  limestones. 


Fig.  15.    Limestone  made  of  Shells. 

If  we  look  closely  at  the  structure  of  limestones,  we  see 
that  they  have  several  different  shapes.  In  the  commoner 
kind  the  mass  of  rock  consists  of  little  grains  as  fine  as 
mud,  and  mingled  with  them  we  can  almost  always  find 
some  small  bits  of  shells,  or  corals;  sometimes,  .though 
rarely,  the  bones  of  fishes  and  quadrupeds.  This  rock  is 


LIMESTONE.  39 

usually  quite  solid.  If  we  burn  it,  a  great  quantity  of 
carbonic  acid  gas  and  some  steam  escapes,  and  we  have 
the  lime  used  in  making  mortar.  If  we  put  it  in  certain 
acids,  the  lime  is  dissolved,  and  there  remains  some  clay  or 
mud,  just  like  that  we  find  in  clay-stones. 

To  see  the  way  in  which  these  limestones  are  formed, 
we  should  go  to  the  tropical  seas  of  the  world,  where 
the  warm  water  holds  a  great  deal  of  animal  life.  Most  of 
the  creatures  living  in  those  seas  have  a  certain  amount 
of  lime  built  into  their  bodies.  Sometimes  this  lime 
serves  as  a  protection  to  the  body  of  the  animal  against 
its  foes,  as  is  the  case  with  all  the  shell-fishes  or  mollusks, 


Fig.  16.    Limestone  Building  Corals. 

or  as  a  solid  support  for  a  community  of  polyps,  as  in  the 
branched  corals ;  sometimes  as  a  skeleton,  to  support  the 
soft  parts  of  the  body,  as  in  the  true  fishes.  When  death 
overtakes  these  creatures,  their  heavy  skeletons  fall  upon 
the  sea-floor.  On  this  floor  there  is  a  host  of  animals  that 
get  their  living  by  eating  these  remains  of  other  animals. 
They  bore  them  through  and  through,  and  finally  reduce 
them  to  a  limestone  mud.  Only  now  and  then  do  we  find 
specimens  that  have  been  well  preserved ;  but,  if  we  ex- 
amine it  with  a  microscope,  we  see  that  almost  any  bit 
of  the  limestone  shows  that  it  has  been  alive. 

Some  of  these  lime-gathering  animals  grow  very  fast. 
An  oyster  as  big  as  a  man's  hand  may  grow  in  a  year  or 


40  THE  MAKING  OF    HOCKS. 

two;  a  great  mass  of  coral  branches  may  be  made  in  a 
few  years,  so  that  the  amount  of  the  lime  that  is  brought 
by  them  to  the  sea-floor  is  in  some  places  very  great. 

The  coral  reefs  are  among  the  most  active  in  this  work  of 
building  limestones.  These  coral  reefs  are  the  most  won- 
derful things  that  the  seas  contain,  rich  as  they  are  in  strange 
creations.  They  are  found  in  two  forms :  as  strips  along 
the  shores  of  the  continents  and  islands,  called  "  fringing  " 
or  "barrier  reefs,"  or  as  solitary  islands  far  out  in  the  deep 
seas,  called  "atols."  The  figures  give  an  idea  of  the  shape 
of  these  reefs.  The  corals  that  make  them  are  star-shaped 


Fig.  17.    Barrier  Keefs  and  Section  of  same. 

animals  that  are  akin  to  our  sea-anemones.  They  live 
in  colonies,  their  bodies  united  together  resembling  a  bush 
with  many  buds  on  its  several  stems.  Each  colony  has  a 
framework  of  limestone,  like  those  shown  in  the  figures. 
Some  of  these  frameworks  are  so  strong  that  they  with- 
stand the  beat  of  the  greatest  waves  that  the  broad  oceans 
hurl  against  them.  Wherever  the  ocean  sends  currents 
of  warm  water  against  the  shores,  these  coral  reefs  abound. 
On  the  eastern  shore  of  Australia  there  is  one  over  a  thou- 
sand miles  long.  In  the  Pacific  and  Indian  Oceans  are 
thousands  of  islands  built  by  coral  animals.  These  have 
been  formed  around  volcanic  or  other  islands,  that  have 


LIMESTONE.  41 

slowly  sunk  down  into  the  sea,  while  the  corals  have  stead- 
ily built  up  towards  the  surface.  They  are  generally  ring- 
shaped,  with  a  bit  of  still  water  fenced  around  with  the 
ridge  of  coral.  The  way  in  which  these  coral  islands  are 
formed  is  shown  in  the  figures. 

Each  of  these  great  coral  towers  of  the  sea  is  alive  only 
at  the  top,  and  for  a  hundred  feet  or  so  below  the  water; 
but  this  crown  of  living  corals  supplies  a  vast  amount  of 
limestone  to  the  sea.  The  waves  break  away  branches 
from  the  corals,  and  throw  them  up  on  the  beach  where 
they  are  ground  to  powder.  There  is  a  strong  current 
sweeping  by  these  islands,  which  carries  this  powdered 
lime  away,  to  deposit  it  far 
over  the  sea-floors.  These 
great  reefs  can  grow  only 
where  there  is  a  strong  mo- 
tion to  the  warm  water;  for 
they  need  a  great  deal  of  food, 
which  they  can  get  only  in 
the  sea- water  moving  by  their 

mouths.    As  it  goes  by,  they,  /%  18    AtoiReef. 

with  their  tentacles,  snatch 
at  the  tiny  creatures  that  fill  the  water,  and  take  them 
into  their  mouths.  This  current,  which  generally  runs  at 
the  rate  of  two  to  four  miles  an  hour,  not  only  serves  to 
feed  these  vast  collections  of  polyps,  but  also  to  bear  away 
the  limestone  mud  formed  on  the  shores  of  the  islands 
by  the  beating  of  the  sea-waves. 

These  coral  communities,  or  atols,  as  they  are  termed, 
are  prodigiously  high  and  steep  mountains  rising  from  the 
floor  of  the  deep  ocean.  If  we  could  drain  away  the 
waters  of  the  Pacific  Ocean,  and  walk  over  its  floor,  we 
should  see  them  rising  like  great  towers,  with  sides  so 


42  THE  MAKING  OF    ROCKS. 

steep  that  we  could  hardly  climb  them ;  and,  on  their 
broad,  flat  tops,  a  shallow  cup,  as  is  shown  in  the  figures. 
We  do  not  know  just  how  many  of  these  coral  islands 
there  are,  but  it  is  likely  that  there  are  over  five  thousand, 
and  they  may  number  ten  thousand.  If  we  include  with 
them  the  reefs  that  are  fixed  to  the  shores,  their  coast 
lines,  if  put  together,  would  probably  stretch  for  a  hun- 
dred thousand  miles.  On  all  these  shores  the  waves  are 
ever  beating,  making  clouds  of  fine  mud  that  stream  over 
the  seas,  and  fall  to  the  bottom  to  make  limestones. 

These  coral  reefs  are  no  new  things  on  the  earth.    From 
very  remote  ages  the  seas  have  been  beating   on   their 

shores,  and  taking  the  lime 
that  they  separated  from  the 
waters,  and  building  rocks  of 
it.  Nor  are  they  the  most 
powerful  agents-  of  making 
limestones,  though  they  are 
by  far  the  most  grand  exam- 
ples of  the  power  of  life  in  its 
work  on  the  earth's  surface. 
Still,  these  coral  reefs  do  not 

make  the  most  of  the  lime  deposits.  The  greater  part  of 
the  limestone  making  is  done  by  the  smallest  and  simplest 
forms  of  life,  that  live  scattered  through  the  sea-water,  or 
on  the  floors  of  the  oceans.  Of  these  creatures  there  is 
an  amazing  variety.  Thousands  of  species  contribute  to 
the  work,  each  by  giving  its  particular  form  of  body  to 
make  up  the  mass  of  the  sediment  that  comes  direct  to 
the  sea-floor  and  makes  limestones.  The  most  effective  of 
these  limestone  makers  are  certain  very  simple  animals, 
called  "  foraminifera."  These  creatures  are,  as  far  as  our 
limited  means  of  knowing  go,  mere  bits  of  living  jelly, 


LIMESTONE.  43 

without  mouths,  stomachs,  or  any  senses ;  but  they  form 
about  them  beautiful  shells  of  lime,  showing  that  they 
are  really  far  more  complicated  than  they  appear.  These 
foraminifera  live  in  myriads  in  the  sea-water,  from  pole  to 
pole,  and  when  they  die,  their  shells  fall  like  little  flakes 
of  snow  down  on  to  the  sea-floor  in  a  slow  shower  that  has 
probably  never  ceased  since  the  earliest  ages. 

On  the  sea-floor  there  are  many  other  forms  that  make 
a  great  deal  of  lime.  There  are  small  solitary  corals,  like 
those  shown  in  the  figures,  and  sometimes  fields  of  crinoids, 
standing  like  tall  grain  with  branching  heads  tangled  to- 
gether. All  these  and  many  more  shells,  corals,  etc., 
kinds  that  cannot  be  noticed 
here,  make  up  the  multitu- 
dinous'life  of  the  sea-floor. 
They  all  give  something  to 
the  great  work  of  making 
rocks.  All  the  while  this  lime 
is  heaping  upon  the  sea-floor, 
there  is  a  steady  rain  of  mud 
upon  it,  some  floating  out 
from  the  rivers,  some  sent  to  fiy.  20.  Radioiaria. 

the  sea  from  the  volcanoes.  This  mingles  with  the  lime, 
and  makes  the  clay  which  we  find  even  in  the  finest  lime- 
stones. If  the  lime  gathers  slowly,  the  clay  will  be  per- 
haps the  larger  part  of  the  rock;  if  the  lime  gathers  fast, 
the  clay  will  be  a  smaller  part  of  the  whole,  so  making 
anything  from  pure  clay  to  pure  limestone. 

Of  all  the  rocks  we  see  on  the  surface  of  the  earth,  the 
limestones  form  not  less  than  one-sixth  part ;  so  the  work 
of  animal  life,  in  building  the  earth's  crust,  is  to  be  com- 
pared with  the  work  of  rivers  or  the  sea-shores. 

In  many  limestones  we   have  great   changes  brought 


44  THE   MAKING   OF    ROCKS. 

about  in  their  appearance  by  the  action  of  heat :  they  are 
turned  into  marble.  Marble  is  crystallized  limestone. 
Heat,  which  often  finds  its  way  into  rocks,  and  water  that 
is  always  in  them,  cause  this  change.  When  it  turns  to 
marble,  the  limestone  no  longer  shows  the  fossils  we  com- 
monly see  in  it.  They  have  all  been  dissolved  and  made 
over  in  the  process  of  crystallizing. 

With  so  much  lime  always  going  into  the  frames  of 
animals,  and  at  their  death  on  to  the  sea-floor,  the  water 
of  the  oceans  would  soon  become  too  poor  in  this  sub- 
stance to  sustain  the  life  it  holds,  but  for  the  means  that 
are  arranged  for  its  supply.  This  continuous  supply  is 
accomplished  in  the  following  way :  Every  drop  of  water 
that  falls  on  the  lands  has  a  certain  power  of  dissolving 
lime.  When  this  water  goes  through  the  earth,  it  takes 
up  from  the  decaying  plants  a  certain  amount  of  a  gas  they 
give  off,  called  "carbonic  dioxide."  This  is  the  gas  used 
in  making  soda  water,  and  is  what  gives  the  suffocating 
power  to  burning  charcoal.  The  earth  holds  a  great  deal 
of  it,  as  we  can  see  in  the  case  of  wells  that  often  fill  with 
"  bad  air,"  which  is  this  gas.  Water  eagerly  sucks  in  this 
gas ;  and,  when  charged  with  it,  can  easily  dissolve  the 
hardest  limestone,  as  it  dissolves  sugar  or  alum,  and  many 
other  substances.  We  often  see  this  lime  gathering  around 
the  places  where  springs  come  out  of  the  earth.  Their  water 
will  often  encrust  anything  put  into  it  with  a  thick  coating 
of  lime.  In  this  way  the  springs  bring  to  the  rivers  a  vast 
quantity  of  lime,  which  constantly  restores  to  the  sea  the 
element  that  the  animals  fix  in  the  limestone  beds.  As  this 
lime  is  completely  dissolved  in  the  water,  it  does  not  set- 
tle to  the  bottom,  but  remains  floating  about  in  the  sea, 
until  it  is  taken  out  by  the  living  creatures  that  require  it 
to  make  their  skeletons.  In  the  course  of  ages,  this  lime, 


LIMESTONE.  45 

now  being  laid  down  on  the  sea-floor,  may  be  lifted  up 
until  it  is  above  tne  level  of  the  sea,  where  it  in  turn  will 
be  dissolved  by  the  rain-water,  and  borne  back  to  the  deep. 

We  see  at  once  how  great  the  changes  of  the  earth 
must  be,  to  have  lifted  to  our  mountain  tops  these  lime- 
stones that  are  now  furnishing  the  lime  that  goes  into  the 
ocean ;  and  we  know  that  we  may  look  forward  to  even  as 
great  changes  in  the  time  to  come,  when  limestones  now 
building  on  the  sea-floor  shall  be  raised  to  the  tops  of 
mountains  that  have  not  yet  begun  to  form. 

It  is  not  until  we  come  to  study  our  soils  that  we  know 
how  much  we  owe  to  these  little  creatures  that  have  sepa- 
rated the  lime  from  the  water.  Wherever  we  find  lime- 
stone rocks,  there  we  have  soils  of  rare  fertility;  for  the 
reason  that  lime  is  a  very  essential  thing  to  most  of  our 
crops,  especially  to  grain,  and  because  the  same  creatures 
that  take  out  lime  from  the  sea-water  separate  several 
other  things  that  serve  to  enrich  soils.  The  most  impor- 
tant of  these  is  phosphorus.  This  is  the  substance  we 
know  so  well  in  lucifer  matches ;  but  it  .has  a  very  great 
use  when  combined  with  lime,  as  it  enters  into  the  bones 
and  bodies  of  all  the  higher  animals ;  without  it  man  could 
not  live. 

The  fact  is,  the  rain-water  that  passes  through  the  soil 
takes  out  of  it  something  of  all  the  substances  that  the 
earth  contains,  and  takes  them  to  the  sea  ;  and  the  river 
waters  are  in  this  way  constantly  carrying  a  little  of  all  our 
metals  to  the  oceans.  From  the  sea,  the  animals  and  sea- 
weeds take  these  substances,  and  build  them  into  rocks 
upon  the  sea-floor.  Some  of  these  rocks  we  see  have  been 
lifted  upon  the  dry  land,  and  these  substances  are  again 
carried  back  by  the  rain-waters  to  the  sea.  So  the  particles 
move  in  an  eternal  circle  from  the  sea-floor  to  the  land,  and 
thence  back  to  the  ocean. 


46  THE  MAKING  OF    ROCKS, 

LESSON  V. 
COAL. 

THE  next  chapter  that  we  shall  study  in  the  history  of 
the  rocks  concerns  coal.  We  have  just  seen  that  the  ocean 
life,  both  plant  and  animal,  is  constantly  doing  a  great 
work  in  the  building  of  the  rocks.  In  coal  we  have  a  like 
work  done  by  plants  upon  the  land.  Looking  at  coal  with 
the  microscope,  we  find  that  it  always  consists  of  a  black 
mass  of  vegetable  matter,  generally  rather  hard  and  shining. 
Further  study  shows  us  that  there  are  various  kinds  of 
coal,  which  range  all  the  way  from  soft  peat,  that  we  may 
find  in  any  swamp,  through  lignite,  that  is  like  peat,  a 
harder  coal,  to  bituminous  coal,  which  is  soft,  and  burns 
with  a  long  flame ;  or  cannel  coal,  that  is  like  it,  only  more 
flaming;  then  to  anthracite,  that  is  yet  harder,  has  no 
flame,  and  is  to  be  burned  only  with  a  strong  draft ;  finally 
to  plumbago,  that  is  so  changed  that  it  can  no  longer  be 
burned  by  any  heat  that  we  can  readily  apply  to  it. 

To  understand  the  history  of  these  various  kinds  of 
coal,  we  must,  for  our  first  lesson,  go  to  the  forests  and 
see  what  goes  on  there.  Every  plant  is  a  contrivance  for 
separating  carbon  from  the  air.  The  leaves  of  the  trees 
and  bushes  gather  this  carbon  from  the  air  that  sweeps  by 
them,  as  the  corals  of  the  sea  gather  their  food  from  the 
ocean.  This  carbon  they  find  in  the  air  in  union  with 
oxygen,  forming  carbonic  acid  gas.  The  oxygen  they  set 
free ;  the  carbon  they  fix  within  their  bodies.  From  the 
soil  they  take  water,  and  a  little  of  various  substances,  — 
potash,  soda,  lime,  etc. ;  but,  of  these  solid  substances, 
they  take  only  somewhere  about  the  fiftieth  part  of  their 


COAL. 


47 


weight.  If  we  cut  down  a  forest,  and  burn  it,  the  part 
that  goes  away  in  flame  and  smoke  came  from  the  air ; 
only  the  ashes  came  from  the  ground.  When  the  trees  die 
and  fall  to  the  ground,  or  when  their  leaves  and  branches 
fall,  they  do  slowly  what  we  do  quickly  by  burning,  —they 
give  their  carbon  back  to  its  union  with  oxygen,  and  in 
this  form  it  again  becomes  invisible  in  the  air.  In  an  or- 
dinary forest  this  process  is  always  going  on.  The  old 
trees,  as  well  as  their  branches  and  leaves,  which  are  con- 
stantly tumbling  down,  fall  into  the  tangle  of  decaying 
matter  that  makes  the  forest-bed,  and  then  rot,  or,  in 
fact,  slowly  burn,  leaving  only  their  ashes.  Usually  this 
goes  on  for  ages.  The  living 
roots  are  below,  the  living 
trunks,  branches,  and  leaves 
above,  and  between  them 
this  layer  of  decayed  mat- 
ter, where  the  dead  parts 
are  taken  back  into  dust,  or 
given  to  the  air  by  decay. 
We  know  that  the  oldest 
forest-tree  lives,  perhaps,  a 
thousand  years  ;  many  of 
them  take  but  four  genera-  ^-21-  Rocks,  Sub-soil,  and  Mould, 
tions  in  two  thousand  years,  so  that  some  trees  now  living 
may  be  only  the  grand-children  of  those  that  lived  when 
Christ  was  born.  Yet  we  know  enough  of  our  forests,  to 
say  that,  in  many  of  them,  time  enough  for  five  or  ten 
thousand  such  generations  to  live  and  die  has  gone  by 
since  they  began  to  be,  yet  the  decayed  forest-bed  is  at 
most  only  a  foot  or  two  thick. 

If  all  the  trunks,  leaves,  and  branches  that  have  decayed 
in  our  ancient  forests  could  have  been  heaped  up  unde- 


48  THE  MAKING  OF    BOCKS. 

cayed  in  a  solid  mass,  we  should  have  beds  of  wood  thou- 
sands of  feet  thick  where  we  now  find  only  a  few  inches 
of  black  mould.  But,  in  place  of  staying  in  the  shape  they 
have  when  they  fall,  all  those  parts  of  trees  by  decay  give 
their  carbon  back  to  the  air,  whence  it  returns  again  and 
again  to  the  plants. 

It  is  interesting  to  consider  that  the  same  little  particle 
of  carbon  now  drifting  about  in  the  moving  air,  may  at  one 
time  be  fixed  in  the  branches  of  a  tropical  palm,  and  then 
rest  awhile  in  a  lichen  that  grows  nearer  the  pole  than  man 
has  ever  been.  It  may  next  grow  close  to  the  perpetual 


Firj.  22.    Growing  Peat  Swamp. 

snow  of  the  Alps,  to  pass,  when  death  sets  it  free,  to  some 
seaweed  rooted  in  the  caverns  beneath  an  ocean  cliff. 

This  is  the  state  of  the  dry  forests.  If  there  is  a  very 
wet  forest-bed,  into  which  the  leaves  and  branches  fall, 
they  do  not  rot,  but  are  preserved  in  the  water.  Wood 
will  rot  when  it  is  partly  wet,  or  at  times  wet,  and  again 
dry ;  but,  if  it  be  buried  in  water,  it  rots  only  in  part,  and 
not  altogether.  The  most  of  its  substance  stays  in  it,  be- 
coming blackened  and  softened,  as  we  see  the  vegetable 
matter  of  swamps,  called  "  peat."  In  any  swamp  we  can 
generally  find  a  great  depth  of  this  black,  half-decayed 
wood ;  but  in  these  swamps  our  ordinary  trees  will  not 


COAT,.  49 

grow ;  it  is  only  small  plants  and  mosses  that  flourish  there. 
Yet,  even  these  little  plants  can  make  very  thick  masses 
of  peaty  matter. 

All  the  northern  countries  have  very  great  and  deep 
bogs  of  this  kind.  Sometimes  the  mass  is  ten,  twenty, 
or  thirty  feet  in  thickness.  This  is  the  first  stage  of 
the  making  of  a  coal-bed:  a  mass  of  woody  matter  kept 
from  complete  decay  by  water,  in  which,  however,  it  be- 
comes black,  softened,  and  matted  together,  until  it  is  like 
a  sponge.  The  next  stage  in  making  coal  is  brought  about 
in  this  way.  The  level  of  the  land  sinks,  or,  what  comes  to 


Fig.  23.    Buried  Peat  Swamp  in  condition  to  become  Coal. 

the  same  thing,  the  sea  rises  until  it  covers  this  mass  of 
peat.  In  this  water  there  are  currents  that  bring  sand 
and  mud  from  tha  shores,  and  bury  the  peat  beneath  a 
thick  layer  of  these  ground-up  rocks.  So  buried,  the  peat 
is  pressed  together  by  the  weight  of  the  rocks  above  it, 
and  gradually  undergoes  changes  that  bring  it  nearer  and 
nearer  to  the  state  of  coal.  If  the  layer  of  beds  laid 
down  upon  it  is  thick  enough,  it  may  become  somewhat 
heated,  which  helps  the  chemical  changes  that  need  to 
go  on.  Coal  has  been  artificially  made  by  placing  woody 
matter,  like  sawdust,  under  a  great  pressure,  while  it 
was  somewhat,  but  not  very  much,  heated.  It  has  also 


50  THE  MAKING   OF    ROCKS. 

happened  that  a  block  of  wood  used  for  a  socket  of  the 
shaft  of  a  water-wheel,  where  it  was  exposed  to  a  friction 
that  could  cause  a  little  heat,  was  found,  after  a  time,  to 
have  changed  into  a  sort  of  coal. 

To  return  to  our  buried  peat  bog.  If  it  is  sufficiently 
pressed  and  changed  by  the  slow  agents  that  time  brings 
into  action,  its  first  shape  is  that  of  brown  coal  or  lignite. 
This  is  rather  more  like  a  coal  than  peat ;  it  burns  with  a 
livelier  flame  and  is  more  solid.  It  is  still  of  a  rather 
brown  than  black  color,  and  is  never  so  heavy  as  coal. 
A  further  step  of  change  produces  the  form  known  as 
bituminous  coal.  In  this  state  the  woody  matter,  still 
further  changed,  often  breaks  into  blocks  with  shining 
faces.  In  the  fire  it  partly  melts  like  wax,  and  it  burns 
with  a  long,  yellowish-white  flame.  There  are  many  varie- 
ties of  it  in  this  stage  of  its  change,  among  which  cannel 
or  candle  coal,  so  called  because  it  burns  with  so  long 
and  steadfast  a  flame,  is  the  most  conspicuous.  This  can- 
nel coal  is  made  from  the  fine  vegetable  mud  that  is  laid 
down  on  the  bottoms  of  the  lakes  in  the  swamps.  We 
can  see  it  forming  in  such  places  at  the  present  day. 
Cannel  coal  does  not  have  the  same  appearance  as  the 
other  bituminous  coal.  It  breaks  in  a  more  irregular  way, 
and  can  be  polished  like  black  marble. 

Still  further  change,  brought  about  by  heat  and  pres- 
sure, makes  what  is  called  anthracite  coal.  This  is  much 
harder  than  the  other  sorts  of  coal,  and  burns  with  very 
little  or  no  flame.  This  is  because  all  the  matter  that  can 
form  gas  has  been  driven  out  of  the  coal,  leaving  only  the 
carbon,  so  that  it  is  like  coke  or  charcoal  in  its  nature. 
We  notice  that  anthracite  is  very  hard  to  burn ;  it  will  not 
take  fire  unless  in  a  good  draft  of  air.  Some  varieties  of 
it  will  not  burn  except  in  close  stoves ;  sometimes  we  find 


COAL.  51 

a  part  of  the  bed  that  cannot  be  burned  at  all.  Still 
further  on  in  the  change,  we  come  to  the  strange  sub- 
stance called  graphite  or  plumbago.  This  is  the  soft 
material  commonly  known  as  black  lead.  It  is  used  for 
making  pencils,  for  which  its  softness  and  blackness  fits 
it;  but  larger  quantities  are  used  for  making  what  are 
called  crucibles.  These  are  pots  for  melting  substances 
that  require  a  very  great  heat,  such  as  steel.  Indeed,  this 
graphite  is  able  to  stand  a  greater  heat  than  fire-brick  or 
any  stone.  Yet  it  is  only  carbon,  exactly  like  that  of  coal, 
that,  in  some  way  unknown  to  us,  but  through  the  action 
of  heat  iteelf,  has  become  incapable  of  being  burned  by 
any  heat  we  can  ordinarily  apply  to  it. 

In  the  coal  field  near  Richmond,  Va.,  we  can  see  ex- 
actly how  the  heat  can  change  coal.  Above  one  of  the 
coal  beds  there  is  a  thin  sheet  of  lava,  which  flowed  there 
after  the  coal  was  formed.  There  is  a  layer  of  several 
feet  of  sandstone  between  the  coal  and  the  lava,  yet  the 
lava,  having  been  as  hot  as  molten  iron,  has  so  baked  the 
coal  that  it  is  changed  into  a  sort  of  anthracite.  In  cer- 
tain places,  where  the  lava  did  not  reach,  the  coal  is  of 
the  ordinary  bituminous  kind. 

Thus,  in  this  wonderful  coal  series,  we  pass  from  the 
living  plant  through  a  succession  of  changes,  that  first 
give  us  the  various  sorts  of  burnable  coals,  and  finally 
this  most  peculiar  substance,  graphite. 

This  making  of  coal  has  been  going  on  throughout  all 
the  great  ages  of  the  earth's  history,  but  there  were  times 
when  a  great  deal,  and  other  times  when  very  little,  was 
made.  In  that  age  of  the  earth's  history  known  as  the 
carboniferous  or  coal  period,  because  of  the  extensive  coal 
beds  that  were  then  deposited,  the  air  of  the  earth  was 
probably  damper  than  now,  and  the  winter's  cold  was  not 


52  THE  MAKING   OF    ROCKS. 

enough  to  kill  delicate  plants,  even  close  to  the  poles. 
Then  the  forests  had  none  of  our  common  trees,  such  as 
oaks,  beeches,  maples  ;  none  of  the  plants  We  see  in  our 
woods  to-day  existed,  but  in  their  place  a  quantity  of  others, 
like  our  club  mosses  and  our  ferns,  but  growing  to  the 
size  of  small  trees.  These  plants  could  grow  with  their 
roots  all  the  time  in  the  water,  which  our  modern  trees, 
with  the  exception  of  the  swamp  cypress  and  mangroves, 
cannot  do.  Besides  this,  their  tangled  roots  and  close-set 
stems  made  a  sponge  that  held  water ;  and  so  the  swamps  of 
the  coal  period  grew  even  on  hillsides,  when  they  were  not 
steep,  as  well  as  on  plains.  The}'  made  peaty  matter  that 
would  turn  into  coal  when  buried.  As  if  to  make  every- 
thing as  it  should  be  for  the  formation  of  coal,  the  lands 
or  the  seas  in  those  days  were  very  unsteady.  The  level 
of  the  oceans  was  often  changed,  so  that  a  great  part  of 
the  continents  was  often  lifted  above  and  buried  beneath 
the  seas.  Thus  to  these  beds  we  look  for  the  greater 
part  of  the  coal  that  is  burned  in  Europe  and  America. 

If  we  examine  a  coal  seam,  we  can  always  find  the  bed 
of  earth  in  which  the  plants  grew ;  above  that  the  bed  of 
coal;  and,  above  all,  the  beds  formed  upon  the  swamp 
sunk  beneath  the  water.  These  beds  are  arranged  one 
above  the  other,  so  that  in  some  countries  there  are  as 
many  as  a  hundred  coal-beds  in  a  thickness  of  less  than 
five  thousand  feet  of  strata. 

Next  to  the  present  soil  of  the  earth,  these  old  buried 
swamps  of  the  earth  are  of  all  the  earth's  resources  the 
most  important  for  man's  welfare.  While  the  present  sur- 
faces give  him  food,  those  old  buried  lands  give  him  heat 
and  power,  which  he  turns  into  infinitely  varied  uses. 

Let  us  consider  a  moment  what  this  heat  and  power 
come  from.  When  plants  grow,  they  do  so  because  they 


COAL.  53 

are  warmed  and  lighted  by  the  sun  that  shines  upon  them 
and  the  air  that  wraps  them  round.  This  force  of  the 
sunshine  they  store  up  in  the  substances  composing  their 
bodies ;  when  we  burn  their  wood,  or  it  decays  in  the 
mould  at  their  feet,  this  force  is  given  back  at  once  to  the 
air.  When  the  woody  matter  is  buried  in  the  coal-bed, 
the  force  is  kept  from  passing  back  to  the  air  —  is  stored 
up  in  a  way  to  be  useful  to  man.  When  we  burn  coal, 
then  we  turn  the  buried  sun  power  of  ancient  times  to  our 
present  uses.  We  warm  ourselves  with  it;  we  make  it 
turn  our  mills;  and,  in  this  manner,  we  have  our  profit  out 
of  the  light  and  heat  of  days  so  far  away  that  we  cannot 
imagine  the  years  that  have  elapsed  since  their  light  has 
ceased  to  shine  and  their  life  to  exist. 

It  is  only  in  the  modern  times  of  man's  history  that  he 
has  used  coal.  Neither  the  Greeks  nor  Romans  nor  He- 
brews knew  anything  of  it.  Its  use  began  in  England  not 
more  than  six  hundred  years  ago,  and  its  great  profit  was 
first  found  in  the  use  of  the  steam  engine.  Now,  the 
chance  of  future  wealth  of  nations  depends  upon  the 
amount  of  coal  they  have  beneath  the  ground  in  their 
territories.  Although  there  is  a  little  coal  in  most  coun- 
tries, the  really  large  and  useful  supplies  seem  to  be 
limited  to  northern  Europe,  where  England  has  the  best, 
to  North  America,  which  is  ten  times  richer  than  Europe, 
to  China  and  Australia.  The  best  that  is  known  is  in 
North  America,  though  the  largest  fields  are  in  China. 
South  America  and  Africa  appear  to  have  but  little.  The 
countries  about  the  Mediterranean,  once  the  richest  and 
most  powerful  in  the  world,  cannot  regain  their  ancient 
place  among  nations  because  they  have  in  their  lands 
scarcely  any  store  of  this  buried  sunshine. 

Thus  we  see  how  the  most  remote  events  of  our  earth's 


54  THE   MAKING   OF   BOCKS. 

history  may  come  to  affect  the  well-being  of  man,  deter- 
mining the  strength  of  peoples  and  the  seats  of  national 
power.  The  fact  that  the  English-speaking  peoples  hold 
the  best  supplies  of  coal,  makes  it  certain  that  their  states 
are  to  have  the  commercial  empire  of  the  earth. 

Besides  the  work  of  storing  up  coal,  plants  and  animals, 
when  buried  in  the  rocks,  may  furnish  by  their  slow 
decay  the  substance  called  petroleum.  This  substance 
is  formed  by  a  slow  chemical  change  in  the  bodies  of 
creatures  buried  in  the  rocks.  These  changes  then  form 
not  only  petroleum  but  a  great  deal  of  gas,  so  that,  when 
we  bore  a  hole  into  the  rocks  where  it  has  formed,  the  gas 
will  drive  the  oil  out  with  great  force.  Most  all  our  rocks 
containing  fossil  animals  or  plants  make  some  of  this  oil, 
but  it  is  generally  pressed  out  by  the  gas  as  fast  as  it 
'forms0,  but  when  there  is  a  continuous  sheet  of  a  very 
dense,  impervious  rock,  such  as  clay  slate,  above  them, 
the  oil  is  retained  until  it  accumulates  in  a  large  quantity, 
so  that  a  well  may  throw  out  two  or  three  thousand  bar- 
rels a  day  whenever  the  rock  in  which  the  oil  lies  is  bored 
into. 

Many  parts  of  the  world  have  furnished  enough  of  this 
coal  oil  to  make  its  gathering  profitable.  For  centuries 
it  has  been  gathered  in  India  and  Japan  by  means  of  com- 
mon wells.  But  the  great  source  of  supply  is  in  western 
Pennsylvania  and  West  Virginia ;  and  there,  small  bored 
wells,  a  few  inches  in  diameter,  are  used  to  get  to  the 
buried  store.  When  the  oil  is  struck,  it  often  blows  the 
boring-rod  to  the  height  of  several  hundred  feet  into 
the  air;  sometimes  this  fountain  catches  fire  and  strews 
destruction  about  it. 

Besides  these  forms  of  buried  force,  laid  down  in  the 
earth  by  animal  and  plant  life,  there  are  many  deposits  of 


COAL.  55 

clay  shale  that  are  full  of  organic  matter,  from  which 
coal  oil  can  be  distilled ;  but,  as  it  is  not  so  cheap  as  that 
from  the  flowing  wells,  they  have  not  been  used  since  the 
flowing  wells  were  found.  One  of  these  beds  of  clay 
shale,  in  the  valley  of  the  Ohio,  extends  over  a  region 
over  one  hundred  thousand  square  miles  in  area,  and 
averages  over  one  hundred  feet  thick.  As  it  contains 
about  one-seventh  of  its  bulk  of  substances  that  can  be 
distilled  into  coal  oil,  it  is  equal  to  a  lake  of  oil  three 
times  as  large  as  Lake  Superior,  having  the  depth  of 
about  fifteen  feet. 

In  these  oil-bearing  clay  shales  there  is  a  store  of  heat 
and  light-giving  materials  that  will  serve  the  uses  of  man 
after  he  has  used  up  all  the  coal  of  the  world. 


CHAPTER  HI. 


THE  WOEK  OF   WATER  AND  AIR. 

LESSON  I. 
THE  AIR. 

WE  have  already  beheld  some  of  those  things  of  the 
earth  that  we  can  grasp  with  our  hands  and  ex- 
amine in  various  other  tangible  ways,  but  we  now  turn  to 
that  unseen  kingdom  of  the  air,  which  more  or  less  affects 
all  that  occurs  upon  the  surface  of  the  earth.  The  air, 
though  invisible,  is  much  like  the  watery  ocean;  it  is 
made  up  of  one  constant  fluid  or  gas  called  nitrogen, 
in  which  are  mingled  smaller  quantities  of  certain  other 
gases,  of  which  the  most  important  are  oxygen,  the  vapor 
of  water,  and  carbonic  dioxide,  or  the  gas  that  oxygen 
and  carbon  commonly  make  when  they  unite.  Because 
the  air  lets  the  light  freely  through  its  substance,  we  do 
not  easily  see  it;  but  when  we  look  at  distant  mountains 
in  the  clear  daylight,  they  usually  look  blue,  and  this 
sky  or  mountain  blue  is  the  color  of  air.  This  great 
ocean  of  the  air  wraps  the  whole  world  about.  It  is 
densest  at  the  surface,  and  grows  thinner  as  we  rise  above 
the  earth,  until,  at  about  fifty  miles  of  height,  it  is  so 
thin  that  it  cannot  well  be  called  air  at  all ;  but  there  is 
no  definite  upper  limit  to  the  air,  —  it  grows  thinner  and 
thinner,  until  it  become  space  or  ether.  There  are  good 
reasons  for  believing  that  this  air  is  composed  of  hummer- 


THE   AIR.  67 

ably  small  particles,  all  dancing  to  and  fro  with  a  great 
speed.  These  atoms  are  so  small  that  if  we  should  take 
the  smallest  bit  we  can  see,  its  bulk  would  contain  mil- 
lions of  these  little  dancing  bodies.  They  move  so  swiftly 
that  they  would  soon  work  away  from  the  earth,  but  that 
they  are  all  held  down  to  the  surface  by  its  attraction. 
Between  these  atoms  there  is  supposed  to  lie  the  yet 
smaller  grains  of  the  matter  called  ether,  which  is  not 
attracted  by  the  earth,  and  so  is  no  thicker  at  the  earth's 
surface  than  in  the  furthest  spaces  between  the  stars. 
This  maze  of  dancing  particles  constitutes  our  air.  It 
would  be  interesting  to  trace  all  that  is  known  of  their 
strange  ways,  for,  though  they  are  invisible,  we  know 
much  about  them  ;  but  we  are  to  look  now  only  at  the 
manner  in  which  the  air  as  a  whole  behaves. 

First,  we  see  that  the  particles  of  air  are  very  easily 
moved.  Swing  the  hand  to  and  fro,  and  we  perceive, 
that  we  can  just  feel  them,  they  slip  so  easily  by.  When 
moved  by  a  strong  wind,  we  feel  them  press  upon  us. 
Next,  we  notice  that  when  heated  this  air  rises.  Look  at 
the  column  of  smoke  over  a  chimney :  it  goes  up  because 
it  is  heated.  Make  a  little  smoke  over  a  stove,  and  see 
how  it  flies  to  the  ceiling.  So  we  perceive  that  a  little 
difference  in  heat  sets  the  air  moving  upwards.  Blow  tha 
smoke  against  a  cold  window-pane,  and  see  how  it  falls  to 
the  floor.  So  we  know  the  cold  sends  the  air  downwards. 
This  air  can  take  a  great  deal  of  water  into  its  tangle  of 
atoms.  Moisten  the  finger,  and  move  it  quickly  to  arid 
fro,  and  we  feel  the  water  evaporate,  and  in  a  few  min- 
utes it  is  dry  ;  the  water,  in  the  form  of  vapor,  has  slipped 
into  the  air,  where  it  is  unseen.  Watch  the  rain  falling, 
and  we  see  this  vapor  of  water,  evaporated  from  sea  and 
land,  turning  back  into  the  liquid  state  again. 


58 


THE   WORK   OF   WATER   AND   AIR. 


On  these  properties  of  the  air,  its  fashion  of  moving  up 
wfrh  heat  and  down  with  cold,  and  of  taking  other  gases 
into  its  mass,  depends,  in  the  main,  all  the  wonderful  work 
it  has  to  do  on  the  earth. 

When  the  sun  rises  high  in  the  heavens  on  a  summer 
noonday,  we  see  it  warms  the  air.  We  can  imagine  that 
under  the  equator,  where  the 
sun  is  nearly  always  over- 
head, the  heat  is  great ;  while 
at  the  poles,  where  it  never 
gets  half-way  up  the  dome 
of  the  sky,  and  for  much  of 
the  year  never  rises,  it  is  very 
cold.  This  greater  heat  at 
the  equater  causes  the  whole 
Fif/,24.  Diagram  of  Air  Currents,  air  that  lies  in  that  region 
•  to  rise  up  from  the  surface.  To  take  its  place,  the -less- 
heated  air,  from  regions  nearer  the  poles,  flows  down 
towards  the  equator.  This  causes  a  down-draft  into  the 
far  northern  and  southern  regions ;  and,  to  replace  the 
descending  air,  there  is  a  current  far  up  in  the  atmosphere, 
blowing  from  equator  towards  the  poles.  This  is  shown 
in  the  figure. 

If  the  earth  were  all  land  or  all  water,  this  would  be 
the  only  general  movement  of  the  air ;  but,  as  its  surface 
is  a  great  ocean,  flecked  over  with  many  lands,  this  great 
current,  from  poles  to  equator  and  from  equator  to  poles,  is 
broken  up,  except  on  the  great  seas.  Under  the  sun,  the 
land  heats  more  rapidly  than  the  sea,  and  so  there  is  gen- 
erally an  up-draft  made  over  all  the  land  when  the  sun  is 
high  in  the  heavens,  and  the  land  warmer  than  the  sea ; 
while  a  down-draft  takes  place  over  the  lands  if  they  are 
colder  than  the  sea.  In  this  manner,  and  by  many  other 


THE   AIR.  59 

differences  of  a  lesser  kind,  the  winds  are  made  variable, 
so  that  we  cannot  reckon  on  their  movements  except  in 
certain  parts  of  the  earth.  But  the  important  fact  about 
the  air  is  that  it  is  always  in  motion ;  for  such  a  thing  as 
a  perfectly  still  air  is  not  known  in  the  world.  Ceaseless 
motion  possesses  it  everywhere  and  at  all  times.  This  fits 
the  air  for  the  important  duty  of  carrying  water  from  the 
seas  to  the  lands.  The  heat  of  the  sun  slips  as  easily 
through  the  air  as  its  light,  and,  falling  on  the  seas,  so 
warms  them  that  they  give  a  good  deal  of  vapor  to  the  air ; 
this,  by  the  motion  of  the  air  currents,  is  borne  off  over 
the  lands,  where  it  falls  in  the  shape  of  rain ;  so  that  the 
first  duty  of  the  air  is  that  of  a  rain  carrier,  bringing  the 
water  back  from  the  ocean  to  the  land  as  fast  as  it  flows 
out  through  the  rivers.  When  we  look  on  a  stream  like 
the  Mississippi  or  the  Amazon,  its  mighty  tide  rushing 
into  the  ocean,  we  may  see  in  the  heavens  above  the 
channel  througL  which  the  winds  are  constantly  carrying 
the  same  waters,  first  up  from  the  sea  to  the  height  of  sev- 
eral miles,  then  in  the  sailing  clouds,  along  through  the  air 
for,  it  may  be,  thousands  of  miles,  to  the  lands  where  it 
falls  as  rain.  This  eternal  circle  of  the  waters  has  been 
traversed  thousands  of  times  by  every  atom  of  water  in 
the  world.  On  this  endless  journey  of  the  waters  de- 
pends the  whole  system  of  feeding  the  life  of  the  sea  and 
land.  The  land  life  could  not  live  without  the  rain,  and 
the  sea  life  would  not  be  able  to  live  without  the  rivers 
bringing  back  to  the  ocean  the  things  that  are  stored  in 
the  rocks  of  the  land.  So  the  life  of  all  the  world  is  kept 
in  being  by  this  circuit  of  the  waters. 

The  next  important  work  of  the  air  is  to  furnish  a 
blanket  to  keep  out  the  outer  cold.  Life,  as  we  know, 
cannot  exist  when  water  is  constantly  frozen.  Only  the 


60  THE   WORK   OF   WATER   AND   AIR. 

birds  and  mammals  (animals  that  suckle  their  young)  can 
live  at  all  in  a  temperature  below  32°  F. ;  but  ten  miles 
above  the  earth  there  is,  and  always  has  been,  a  cold  of 
below  zero.  But  for  the  air,  this  cold  would  descend 
upon  and  stay  on  the  earth.  There  would  be  no  night 
even  in  summer  and  under  the  equator,  where  the  tem- 
perature would  not  fall  to  zero  or  below  it.  The  air  pro- 
tects the  earth  in  this  way.  The  heat  that  falls  from  the 
sun  goes  through  the  air  with  ease,  as  it  does  through  a 
pane  of  glass ;  but,  when  it  warms  the  earth,  this  heat  it 
gives  to  the  surface  cannot  go  back  as  easily,  especially  if 
the  air  have  some  vapor  of  water  in  it,  as  it  always  has. 
This  heat  that  has  fallen  in  the  day  will  not  be  able  to  go 
back  into  space  during  the  night,  but  is  held  upon  the 
earth.  Thus  the  air  is  a  trap  into  which  it  easily  enters, 
but  escapes  with  difficulty.  This  work  of  blanketing  the 
earth  against  the  outer  cold  is  one  of  the  most  important 
effects  of  the  air. 

Yet  another,  and  one  more  important  work  of  the  air, 
is  to  supply  oxygen  to  animals  and  carbon  to  plants. 
Both  these  gases  are  borne  on  the  air,  but  in  different 
proportions.  About  one-fifth  the  whole  weight  of  the  air 
is  oxygen,  but  only  about  one  two-hundredth  is  carbonic 
dioxide,  or  gaseous  carbon.  As  the  air  goes  by  animals 
and  plants,  they  take  what  they  need  of  these  gases.  The 
animal  takes  the  oxygen  by  its  breathing  organs,  and  gives 
back  to  the  air  carbonic  dioxide.  The  plant  takes  this 
carbon  and  oxygen  combined,  separates  the  two,  and  gives 
back  the  oxygen  to  be  carried  until  it  is  needed  by  ani- 
mals. Even  in  the  sea,  every  plant  gets  its  carbon  from 
this  gas,  which  is  mingled  in  the  water ;  and  every  animal 
breathes  by  taking  the  air  that  is  always  similarly  mingled 
in  the  oceans.  If  we  boil  some  water,  and  then  put  a 


AIR.  61 

fish  or  any  other  water  animal  in  it,  it  will  die ;  for  boiling 
drives  out  the  air  that  is  in  water.  If  we  pour  the  boiled 
water  from  one  vessel  to  another  for  a  few  times,  the  air 
will  be  again  entangled  in  it,  and  the  creatures  will  be 
able  to  breathe. 

Thus  we  see  that  the  universal  wrap  of  air  that  the 
earth  has  about  it  serves  as  a  great  medium  of  exchange 
in  the  work  of  the  world.  Into  it,  after  death,  the  ani- 
mals and  plants  cast  the  store  of  materials  which  they 
took  from  it  while  alive.  If  they  decay  on  the  surface  of 
the  earth,  they  quickly  give  it  back  ;  if  they  are  buried  as 
fossils,  these  substances  taken  from  the  air  may  be  con- 
verted to  coal  or  petroleum ;  and  only  after  a  long  time 
return  to  the  great  storehouse  of  the  air,  to  be  ready  for 
the  use  of  other  living  things. 

In  this  way,  from  the  ancient  ages,  the  air  has  always 
been  ready  to  lend  the  things  that  make  up  the  largest 
part  of  animals  and  plants,  taking  them  back  in  time  for 
the  use  of  other  creatures.  As  the  great  agent  of  trans- 
portation, the  water  carrier,  the  heat  carrier  that  brings 
the  sinews  of  life  to  every  creature  of  the  land,  the  air  has 
given  to  everything  that  has  ever  lived  the  first  condition 
of  its  existence. 

We  have  only  touched  on  the  principal  duties  of  the 
air,  but  we  have  seen  enough  to  show  us  that  this  scarcely 
visible  element,  that  seems  to  be  the  merest  thing  of 
chance,  has  most  important  duties  in  the  work  of  the 
world,  and  does  them  with  wonderful  perfection. 


62  THE    WORK   OF   WATER   AND   AIR. 

LESSON  II. 

THE  WORK  OF  WATER. 

THE  greater  ocean  of  the  air  wraps  the  whole  world 
about.  The  other  great  fluid,  water,  covers  only  about 
three-quarters  of  the  surface.  Though  the  oceans  are 
smaller  in  size  and  less  deep  than  the  air,  they  weigh 
more  than  all  the  atmosphere.  At  most,  air  presses  with 
a  weight  of  only  fourteen  pounds  to  the  square  inch  ;  but 
in  the  deeper  seas  the  water  presses  with  a  weight  of  hah 
as  many  tons  on  an  equal  surface.  These  two  mobile 
parts  of  the  earth,  the  gaseous  air  and  the  fluid  water, 
rule  the  earth's  surface.  Almost  everything  that  happens 
here  is  due  in  some  degree  to  their  work. 

Let  us  consider  how  water  does  its  work.  We  have 
already  seen  a  good  part  of  this  work  in  tracing  the  his- 
tory of  pebbles,  sand,  mud,  etc.,  so  what  we  have  now  to 
do  is  to  show  the  work  done  by  water  that  does  not  ap- 
pear in  the  history  of  those  things. 

Foremost  of  all  its  work,  we  must  place  the  power  of 
water  to  dissolve  all  things.  Some  it  takes  up  easily,  as, 
for  instance,  all  the  different  sorts  of  salt;  but  all  the 
other  things  of  the  world,  even  the  least  soluble  metals, 
yield  to  the  water  something,  which  it  conveys  to  the 
seas.  What  water  cannot  do  of  itself  alone  in  the  way 
of  dissolving,  it  manages  to  effect  when  it  gets  charged 
with  carbonic  dioxide  gas,  as  it  does  in  the  decaying 
mould  of  our  forests  and  elsewhere.  In  one  way  and 
another,  it  gets  even  such  metals  as  gold  and  silver  into 
solution,  though  in  small  quantities.  To  this  power  that 
waters  have  of  dissolving  all  substances  we  owe  the  pos- 


THE    WORK   OF   WATER.  63 

sibility  of  animal  and  vegetable  life.  Plants  and  animals 
grow  and  live  through  their  circulations.  Currents  of 
water  in  the  shape  of  sap  or  blood  carry  numerous  sub- 
stances through  their  forms,  which  are  built  into  their 
frames.  The  same  currents  of  water  bear  away  the  waste 
or  dead  parts  of  the  living  structure  back  into  the  outer 
world. 

In  the  life  of  the  whole  earth,  as  in  the  life  of  an  ani- 
mal or  a  plant,  water  is  the  great  means  of  carriage.  By 
its  motion  food  is  brought  to  the  creatures  of  the  sea,  and 
the  matter  thrown  out  by  volcanoes,  or  brought  to  the  sea 
by  the  rivers,  is  carried  to  the  place  where  it  is  to  be 
built  into  new  strata  on  the  sea-floor. 

In  its  large  work  of  carriage,  water  is  charged  with  the 
conveying  of  heat  from  one  region  to  another.  The  cur- 
rents of  the  oceans  take  the  hot  water  from  the  tropics  to 
the  poles,  and  the  cold  water  of  the  poles  to  the  tropics ; 
and  thus  make  the  earth's  climate  far  more  uniform  than  it 
would  otherwise  be.  The  Gulf  Stream,  that  great  current 
which  flows  northward  in  the  Atlantic  from  the  Gulf  of 
Mexico,  carries  more  warmth  to  the  Arctic  regions  than 
comes  to  them  from  the  sun.  This  circulation  of  water 
in  the  seas  is  not  unlike  the  movement  of  the  blood  in 
our  own  bodies.  As  blood  carries  food  and  warmth  to  all 
the  bodily  parts,  so  this  system  of  the  waters  in  the  ocean 
streams,  clouds,  and  rivers,  nourishes  and  warms  the  whole 
life  of  the  earth. 

There  are  many  of  these  great  streams  of  the  ocean 
flowing  in  circling  currents,  warm  from  the  tropical  re- 
gions towards  the  poles,  and  cold  from  the  polar  regions 
to  the  tropics.  But  for  the  great  stream  of  heat  they 
carry  from  near  the  equator,  the  tropical  countries  would 
be  too  hot  for  man  to  live  in,  and  all  northern  Europe  and 


04  THE    WORK   OF    WATER    AND    AIR. 

the  most  of  the  United  States  would  be  so  cold  that  they 
would  be  of  little  use  to  man. 

One  of  the  great  works  of  the  sea  is  in  building  the 
rocks  that  afterward,  lifted  above  its  surface,  form  the 
continents.  This  work  is  constantly  going  on  all  over  its 
bottom.  When  the  great  ocean  currents  sweep  near  the 
land,  they  take  up  a  large  part  of  the  mud  brought 
down  by  the  rivers,  and  bear  it  far  out  to  the  ocean 
depths,  where  it  falls  to  the  bottom,  and  is  built  into 
rocks. 

All  over  the  ocean  bottom  a  host  of  fixed  animals  are 
living  which  are  fed  by  the  water  and  the  things  the  water 
brings  to  them  ;  dying,  the  bodies  of  these  animals  are 
built  into  the  rocks.  Floating  wood  and  seaweed  rot  and 


Fig.  25. 
Coast  Shelf  made  by  the  Tide. 

become  water-logged ;  then  sink  to  the  bottom  to  mingle 
with  the  mud  and  the  remains  of  animals,  the  whole  being 
built  into  rocks. 

Along  the  shore  the  waves  and  the  tide  are  continually 
taking  a  part  of  the  mud  out  into  the  sea,  and  making 
new  stratified  rocks  of  them.  All  along  the  shores 
of  the  continents  there  is  a  submarine  shelf  of  this 
waste  that  the  tide  and  waves  have  borne  away,  which 
makes  a  shallow  belt  of  waters  near  the  shore.  Along 
the  eastern  shore  of  the  United  States  this  shelf  has  this 


THE   WORK   OF   WATER.  65 

Thus,  while  the  sea  is  continually  destroying  the  land 
by  its  waves  and  tides,  or  by  the  water  it  sends  as  rain, 
it  is  always  building  them  back  into  rocks  again,  —  rocks 
which  may  in  time,  perhaps,  be  lifted  into  new  lands. 


66  THE   WORK  OF    WATER   AND  AIB. 

LESSON   III. 

VEINS. 

IF  we  look  closely  at  any  very  old  and  much  changed 
rocks,  we  shall  find  that  they  have  been  divided  by  gashes 
that  cross  the  bedding,  and  that  these  gashes  are  filled 
with  various  stones,  sometimes  containing  metals,  as  gold, 
silver,  copper,  etc.  It  is  from  these  veins  that  come  our 
supplies  of  all  the  metals  used  in  our  arts  except  iron,  so 
they  are  of  a  practical  as  well  as  a  scientific  interest. 

The  first  question  we  ask  ourselves  is  how  the  crevices 
that  hold  the  veins  came  to  be  formed,  and  then  how  the 
minerals  that  fill  them  came  into  their  places. 


Fig.  26.    Ordinary  Fault ;  numbers  show  beds  originally  continuous. 

Veins  are  formed  in  crevices  that  open  in  the  rocks. 
They  are  due  to  different  causes.  Sometimes  they  are  the 
result  of  a  shrinking  of  the  rocks,  something  like  that 
which  takes  place  in  drying  clay;  at  other  times  the 
rocks  having  been  pushed  from  the  sides,  were  forced  to 
break  into  large  fragments,  and  pieces  slipped  over  each 
other,  as  in  Fig.  27. 

When  these  breaks  are  formed,  they  leave  an  opening  in 


VEINS.  67 

the  rocks  which  is  never  very  wide  but  may  be  very  deep. 
This  crevice  is  sometimes  ten  thousand  feet  or  more 
from  top  to  bottom,  and  not-  more  than  a  few  feet  from 
side  to  side.  Some  parts  of  its  walls  generally  rest  against 
each  other,  there  being  at  times  only  a  rambling  crevice 
that  a  mouse  could  hardly  creep  through. 

We  have  now  to  notice  again  that  some  of  the  sea-water 
is  prisoned  in  the  rocks  when  they  are  made,  and  so  is 
often  buried  to  great  depths  beneath  the  surface.  When 
deeply  buried,  this  water  is  very  much  heated  by  the  heat 
that  exists  in  the  depths  of  the  earth.  When  such  a  rent 
is  made  in  the  rocks,  these  deep  waters  find  a  path  to 
the  surface.  It  also  happens 

that  some  of  the  rain-water  fc^aggg^^  ^^  'v* 
that  falls  on  the  earth  often 
finds  its  way  to  great  depths. 
When  in  the  depths,  it  be- 
comes heated,  and  gets  thereby 
great  power  of  dissolving 
various  substances.  We  all 
know  that  water  will  dissolve 

more     of    all    the     substances      Fi<>'21-    Diagram  of  a  Hot  Spring. 

that  it  takes  into  solution  when  hot  than  when  cold. 
After  a  time  this  water  is  urged  towards  the  surface,  and 
generally  creeps  up  along  with  some  of  the  water  that  was 
buried  in  the  rocks  when  they  were  laid  down  on  the  sea- 
floor. 

This  mixture  of  rain  and  sea-water,  by  means  of  its 
salt,  its  high  heat,  and  the  presence  in  it  of  various  gases, 
dissolves  a  portion  of  all  the  substances  it  touches ;  and 
so,  when  it  starts  again  for  the  surface,  it  has  a  great  load 
of  various  minerals  in  its  keeping.  The  easiest  way  for 
it  to  get  to  the  surface  is  through  just  such  rifts  of  the 


68 


THE   WORK   OF    WATER    AND    AIR. 


rock  as  have  been  described.  When  it  starts  upward,  it 
is  at  a  heat  that  may  be  very  much  above  the  boiling 
point  of  water.  In  a  shallow  open  vessel,  water  boils 
at  the  heat  of  212°  F.,  but  if  we  made  the  sides  of  the 
kettle  a  mile  high,  we  should  have  to  raise  the  heat  of  the 
water  at  the  bottom  to  a  high  point  before  the  water 
would  boil.  In  many  cases,  when  the  water  starts  up 
towards  the  surface,  it  has  more  than  a  mile  of  water 
above  it,  and  so  it  can  have  a  very  high  temperature,  —  a 
thousand  degrees  or  more.  Water  at  the  temperature  of 
a  thousand  degrees  cuts  many  stones  like  an  acid,  and 
can  hold  a  wonderful  amount  of  matter  in  solution.  As 
it  creeps  up  toward  the  surface,  it  grows  cooler,  and  has  to 
part  with  a  portion  of  its  bur- 
den. This  is  done  by  laying 
down  certain  minerals  or  met- 
als on  the  sides  of  the  crack 
through  which  it  flows.  After 
a  time,  the  waters  becoming 
cooler,  another  substance  may 
be  laid  down,  and  so  on,  until 
the  way  for  the  water  is  quite 
Fig.  28.  Section  through  a  Vein,  blocked  up.  Ill  this  way  the  ' 

vein  comes  to  appear  in  a  cross-cutting  like  the  figure. 

The  water,  when  it  comes  out  on  the  ground  level,  appears 
as  a  hot  spring.  There  are  many  thousands  of  these  now 
in  the  world,  and  each  may  be  making  a  lode  or  vein  like 
that  shown  in  the  figure.  It  is  only  a  part  of  the  veins 
that  are  made  that  have  any  metallic  matter  in  them.  In 
many  cases  the  water  may  not  have  been  hot  enough  to 
dissolve  the  metals ;  or  there  may  not  have  been  any  in 
the  rocks  through  which  it  passed.  Generally,  however, 
we  shall  find  a  small  quantity  of  metals  in  any  vein,  but  it 


VEINS.  (39 

is  not  likely  to  be  great  enough  to  pay  the  miner  for  his  la- 
bor in  getting  it  out.  We  find,  when  we  study  hot  springs, 
ample  proof  that  this  explanation  of  the  process  by 
which  veins  are  made  is  true ;  gold  and  other  metals  have 
been  found  in  their  waters,  and  they  deposit  about  their 
mouths  just  such  stones  as  we 
often  find  in  veins ;  besides 
these,  very  hot  springs  are 
oftenest  found  in  the  regions 
which  are  rich  in  valuable 
mineral  deposits.  The  great 
Comstock  Lode,  which  has 
produced  more  silver  than  any 
other  in  North  America,  and  ™"  "'~^~ 

more     gold     than     any    Other       Sandstone  becoming  Mineralized. 

mine  in  the  world,  is  still  the  pathway  of  hot  springs. 
The  miners  are  constantly  fighting  water  hot  enough  to 
scald  the  skin. 

There  are  other  ways  in  which  deposits  somewhat 
like  veins  are  formed.  Sometimes  the  hot  water  from 
below,  trying  to  find  its  way 
to  the  surface,  creeps  upward 
through  a  steep  sloping  bed  of 
rock  which  is  porous  enough 
to  allow  the  water  to  crawl 
through  it. 

In    Fig.   29  the   bed   A   is 
supposed    to  be  a  sandstone 
or  a   pudding  stone  through 
which     the    water    can    rise        Fiy.ao.  Hot  Spring  Caverns, 
slowly  to  the  surface ;  the  metals  will  then  be  gathered  in 
the  little  spaces  between  the  stones  or  sand-grains  as  it  is 
in  a  vein.     Sometimes,  also,  the  waters  of  hot  springs,  as 


70  THE   WORK    OF    WATER   AND   AIR. 

they  climb  towards  the  surface,  eat  out  caves  in  the  rocks, 
especially  if  they  be  limestones;  in  the  course  of  time, 
when  the  waters  are  less  hot,  they  may  fill  these  caverns 
with  mineral  deposits,  such  as  gold  and  silver  ores.  Some 
very  valuable  deposits  of  this  sort  have  been  found  in 
the  Rocky  Mountains. 

In  the  countries  where  there  are  mineral  veins,  but  no  hot 
springs  at  present,  we  find  proof  that  the  veins  were  formed 
a  long  time  ago,  giving  time  for  the  movement  of  hot 
waters  to  cease. 

The  powers  of  destruction  go  always  hand  in  hand  with 
the  powers  of  construction.  These  veins  are  not  long  formed 


Fill.  31.    Wearing  dowu  of  Land ;  dotted  lines  show  ancient  surface. 

before  they  begin  to  wear  away  under  the  action  of  rain, 
frost,  or  glaciers.  If  the  veins  hold  gold  or  platinum,  these 
metals  being  heavy  and  hard  to  dissolve  or  rust,  they  are 
often  found  gathered  in  the  beds  of  the  streams  mixed 
with  the  gravel  and  sand ;  but  all  the  other  metals  are 
easily  rusted,  i.e.,  combined  with  oxygen,  in  which  state  they 
may  be  dissolved  in  the  water  and  washed  away  to  the  sea. 
Even  the  gold  and  platinum  gradually  go  into  the  water, 
and  are  borne  to  the  sea ;  once  in  the  sea-water  they  stay 
there  for  a  long  time.  When  the  sea-water  evaporates, 
these  metals  cannot  rise  up  to  the  clouds  with  it ;  the  only 


VEINS.  71 

way  out  of  the  water  is  through  the  bodies  of  animals  and 
plants.  These  creatures  each  take  a  little  of  the  many 
substances  in  the  sea-water,  and  when  they  die  and  decay, 
leave  this  little  locked  up  in  the  mud  on  the  sea-floor  into 
which  their  remains  pass.  This  mud  is  slowly  changed  to 
rock,  and  in  time  may  be  lifted  into  the  air  again.  These 
rocks  have  veins  formed  in  them  again ;  the  metals  may 
be  once  more  gathered  into  the  crevices,  and  again  worn 
away  by  the  rivers  and  carried  to  the  sea. 

This  is  another  of  the  circles  of  change  through  which 
water  leads  the  things  of  the  earth.  And  here,  as  in  many 
others,  life  has  a  share  in  the  work.  Every  particle  of 
gold  we  see  may  have  been  several  times  through  this  slow 
journey  from  the  sea-water  to  the  living  being ;  thence  to 
the  sea  mud ;  thence,  in  turn,  to  compacted  stone ;  then 
to  the  vein ;  and,  finally,  by  way  of  the  mountain  streams, 
back  to  the  sea. 

Only  a  very  small  part  of  the  gold,  silver,  tin,  lead,  or 
other  metals  that  get  into  the  rocks  finds  its  way  into  veins  ; 
by  far  the  larger  part  is  never  so  gathered  together  in  veins, 
but  stays  in  the  scattered  form  in  the  rocks,  and  goes  back 
to  the  sea  when  they  are  worn  away. 

There  is  another  way  in  which  these  fractures  are  some- 
times filled.  In  place  of  various  mineral  substances  de- 
posited by  water,  the  crevice  becomes  charged  with  molten 
rock, — lava,  as  it  is  commonly  called, — which  is  crowded 
into  the  space.  When  filled  with  this  substance,  its  forms 
are  no  longer  known  as  veins ;  they  are  termed  trap  dykes. 
It  often  happens  that  we  find  a  trap  dyke  and  a  vein  close 
together ;  but  in  the  lava  itself  we  rarely  find  any  valuable 
ores  in  a  shape  to  be  mined.  It  is  not  quite  certain  just 
how  these  trap  dykes  are  formed,  but  this  is  probably  their 
history.  When  the  crevice  forms,  by  the  breaking  apart 


72  THE    WORK   OF    WATER    AND    AIR. 

of  the  rocks,  it  may  extend  down  into  the  earth  to  a 
greater  or  less  depth.  If  it  go  very  deep,  it  may  find  its 
way  to  a  part  where  the  rock  is  heated  so  hot  that  it  can 
flow  like  melted  lead  or  iron.  This  lava  is  squeezed  up 
into  the  crack.  The  pressure  that  drives  it  up  probably 
comes  from  the  steam  that  all  the  deep  rocks  seem  to  hold. 
This  steam  is  held  in  by  the  rocks  that  lie  above  it,  which 
close  it  in  like  the  sheet  iron  of  a  steam-boiler.  As  soon 
as  a  crevice  is  made  above  this  steam,  it  drives  the  molten 
rock  up  into  it.  Generally  these  trap  dykes  are  much 
wider  than  most  mineral  veins.  They  may  also  run 


Fig.  32.    Some  Forms  of  Dykes. 

deeper  into  the  crust  of  the  earth.  In  some  regions  they 
are  exceedingly  plentiful,  there  being  one  every  few  feet 
of  distance  as  we  go  across  the  surface.  We  generally 
can  see  that  the  dyke  stone  has  been  very  much  heated, 
for  it  has  baked  the  walls  of  the  crevices.  At  other  times 
we  find  pieces  of  stone  torn  from  the  sides  of  the  crevice, 
with  sharp  edges  in  the  trap ;  showing  that  it  was  not  hot 
enough  to  melt  them. 

These  dykes  come  into  close  relation  with  the  volcanic 
lavas,  the  only  important  difference  being  that  the  volcanic 
lavas  are  thrown  out  into  the  open  air,  while  these  traps 
were  formed  far  beneath  the  surface,  and  are  therefore  geii- 


VEINS.  73 

erally  much  the  most  solid.  We  shall  see  more  of  these 
lavas  when  we  come  to  study  their  behavior  in  volcanoes. 
It  is  only  because  they  are  often  connected  with  mineral 
veins  that  they  are  touched  upon  here. 

We  have  now  seen  that  underground  water  often  makes 
deposits  of  precious  metals  in  crevices.  We  will  now  turn 
to  the  action  of  water  in  its  rarer  but  even  more  interest- 
ing form  of  working,  when  it  makes  caves  such  as  the 
Mammoth  Cave  in  Kentucky. 


74  THE   WORK   OF   WATER   AND   AIR. 

LESSON  IV. 

COURSE  OF  WATER  UNDERGROUND. 

THE  greater  part  of  the  work  done  by  water  is  done 
above  the  ground ;  but  there  are  certain  peculiar  effects 
it  has,  when  it  works  below  the  surface,  that  have  much 
interest  for  us.  Some  of  these  we  have  noticed  in  the 
history  of  mineral  veins.  There  are,  however,  many  other 
peculiar  results  that  are  of  a  very  different  character. 

When  water  falls  as  rain,  a  part  of  it  flows  at  once  away 
to  the  streams,  and  a  part  penetrates  into  the  earth.  That 
which  goes  below  the  surface  creeps  slowly  through  the  earth 
until  it  is  either  sucked  up  by  the  plants  or  escapes  into 
the  springs.  This  underground  water  that  is  going  towards 
the  springs  generally  cuts  for  itself  little  imperfect  chan- 
nels, by  dissolving  away  the  soil  so  as  to  make  a  natural 
drain,  which  we  imitate  when  we  put  pipes  under  a  field 
for  drainage.  But  these  springs  that  do  not  have  their 
channels  below  the  level  of  the  soil  are  always  very  small, 
and  last  only  during  wet  weather.  When  we  find  a  spring 
with  a  strong  stream  of  water,  we  may  be  sure  that  it 
comes  out  of  the  earth  from  below  the  level  of  the  soil 
after  a  journey  through  the  underlying  rock.  The  ques- 
tion arises,  how  does  it  manage  to  make  a  passage  through 
this  rock?  These  rock  passages  of  the  underground 
waters  are  sometimes  among  the  most  wonderful  of  the 
works  that  water  makes.  If  the  rock  be  one  that  water 
cannot  easily  dissolve,  such  as  sandstone,  claystone,  pud- 
ding stone,  granite,  etc.,  the  only  chance  for  water  to 
make  springs  is  to  get  deep  into  it  through  some  rift  or 
break  in  the  mass  of  rock.  These  are  not  often  found. 


COURSE   OF   WATER    UNDERGROUND.  75 

The  result  is,  that  such  springs  are  rarely  found  in  regions 
underlaid  by  rocks  of  this  sort.  The  most  of  the  surface 
of  New  England,  for  instance,  is  almost  destitute  of  good 
springs  because  it  is  generally  underlaid  by  very  hard 
rocks.  When,  however,  the  underlying  rock  is  limestone, 
we  generally  have  very  many  large  rock  springs  that  carve 
out  for  themselves  great  underground  channels  called  cav- 
erns. These  caverns  are  of  very  diiferent  sizes,  sometimes 
being  small  tube-like  openings  that  are  hardly  large 
enough  for  the  swollen  waters  in  times  of  rain.  These 
occur  when  the  limestone  rocks  are  bedded  with  strata, 


/~.  i  n/^\ 


Fig.  33.    Section  through  Caverns  in  Limestone  Rocks. 

like  claystones  between,  that  are  not  to  be  dissolved  by 
the  water.  When,  however,  the  beds  of  limestone  are 
thick,  and  without  these  clay  partings,  the  caverns  may 
become  very  large  indeed. 

Perhaps  the  largest  of  these  limestone  caves  are  found 
in  Kentucky,  where  there  is  a  region  containing  about 
eight  thousand  square  miles  of  country  that  is  completely 
honeycombed  with  them.  Some  of  these,  such  as  the 
Mammoth  Cave,  are  so  vast  that  we  may  walk  for  days 
through  passages  that  are  often  thirty  feet  or  more  high 


76  THE    WORK   OF    WATER   AND   AIR. 

and  fifty  feet  wide.  Underground  rivers  and  waterfalls, 
chambers  beautifully  ornamented  with  wonderful  stalac- 
tites and  stalagmites,  and  a  great  number  of  animals  that 
live  in  the  cavern  and  nowhere  else,  make  these  chambers 
quite  an  underground  world,  where  everything  differs  from 
the  daylight  region. 

The  way  these  caverns  are  formed  can  easily  be  seen  by 
studying  what  is  now  going  on  in  the  country  where  they 
occur.  This  Kentucky  cavern  district  lies  in  an  elevated, 
level  region,  where  the  rocks  have  never  been  tilted  about, 
but  stay  in  much  the  same  position  as  that  in  which  they 
were  made  on  the  sea-floors,  before  the  coal  time.  When 
we  journey  over  this  country,  we  see  that  only  the  large 
streams  appear  at  the  surface  of  the  ground.  These  flow 
in  deep  gorges,  with  steep  cliffs  on  either  side.  The  smaller 
streams  do  not  flow  on  the  surface.  They  come  into  the 
main  rivers  through  cavern  mouths,  that  often  lie  below 
the  level  of  the  water,  along  these  greater  streams. 

The  surface  of  the  country  between  these  rivers  has  no 
valleys  in  it,  such  as  have  the  streams  in  most  parts  of 
the  earth,  but  is  arranged  in  circular  shallow  pits,  called 
sink  holes,  such  as  are  shown  in  figure.  Of  these 
there  are  often  several  dozen  in  a  square  mile  of  fields. 
All  the  water  that  runs  off  the  surface  in  a  rain  goes  into 
these  sink  holes,  and  flows  down  into  the  earth  through  a 
small,  ragged  tube  that  descends  from  the  centre  of  the 
pit.  We  can  often  hear  it  in  times  of  heavy  rain  run- 
ning down  into  the  depths  of  the  earth.  Some  of  these 
sink  holes  have  large  openings,  so  that  a  brave  explorer 
can  be  lowered  down  into  the  underground  course  of  the 
water.  In  this  way,  we  can  see  the  whole  course  of  the 
cavern  making.  The  sink  hole  is  shaped  as  in  the  figure, 
which  shows  a  sink  hole  and  the  lower  chambers  cut  in 


COURSE    OF    WATER    UNDERGROUND. 


77 


the  thick  beds  of  the  limestone,  which  may  be  as  much  as 
three  hundred  feet  in  height,  from  the  narrow  throat  at 
the  top  to  the  base.  The  entrance  from  the  open  air  is 
generally  very  narrow,  but  with  various  irregularities.  The 
opening  widens  until  it  is  sometimes  as  much  as  fifty  feet 
from  wall  to  wall.  Whenever  there  is  a  strong  shelf  of 
rock,  there  are  generally  level  passages  leading  off  into 
the  distance  towards  the  lower  mouth  of  the  cave.  We 
may  pass  several  of  these  in  the  descent.  When  we  ar- 
rive at  the  bottom,  we  find  a  pit  generally  full  of  water, 
and  by  its  side  another  horizontal  passage  leading  off  into 
the  darkness. 

In  the  bottom  of  this  vertical  chamber  or  dome,  if  we 
look  closely,  we  see  many  bits  of  flint  and  other  hard 
stones.  They  are  not  a  very 
striking  feature  of  the  cav> 
ern,  but  they  are  the  key  to 
a  part  of  its  work.  We  must 
now  conceive  what  happens 
in  wet  weather,  when  down 
this  deep  shaft  the  water 
rushes  with  very  great  force. 
These  hard  stones  are  then 
driven  like  miner's  drills  Fig.  34.  Dome  of  Cave, 

against  the  rock,  and  they  speedily  cut  up  the  soft  lime- 
stone. The  lime  is  easily  carried  away  by  the  stream 
through  the  side  passage.  The  bits  of  flint  themselves 
are  found  in  the  limestone  rock.  We  can  often  see  them 
sticking  out  of  the  walls,  and  the  Indians  were  in  the 
habit  of  coming  to  these  caves  to  get  such  flints  for  their 
arrow-heads. 

Entering  into  the  side  galleries  that  open  out  of  this 
"  dome,"  we  find  that  they  lead  off  horizontally  for  great 


78  THE   WORK   OF   WATER  AND   AIR. 

distances;  sometimes,  as  in  the  great  avenues  of  the 
Mammoth  Cave,  we  can  walk  through  a  passage  as  large 
as  the  aisle  of  a  cathedral  for  four  or  five  miles.  Each  oi 
these  side  passages  or  galleries  gave  a  way  for  the  water 
out  to  the  air,  at  the  time  when  the  dome  had  not  cut 
deeper  than  down  to  the  level  of  the  floor  of  the  particu- 
lar gallery.  The  "domes"  of  these  caverns  are  sometimes 
wonderfully  grand.  The  walls  are  sculptured  by  water 
into  fantastic  likenesses  of  columns.  When  lighted  with 
bright  fires,  it  is  hard  to  believe  that  we  are  not  looking 
upon  some  supernatural  work.  The  galleries,  if  less  grand, 


Jf'iy.  35.   .Part  of  Gallery  nearly  filled  by  Stalactites. 

are  more  beautiful,  and  in  them  are  found  the  finest  speci- 
mens of  those  stalactites  that  are  the  chief  ornament  of 
these  underground  chambers. 

These  singular  structures  are  of  the  most  varied  forms. 
Sometimes  they  are  like  flowers,  clustering  over  the  ceil- 
ings, and  shining  in  the  light  of  the  torches ;  again,  they 
are  like  the  trunks  of  trees  growing  from  the  floor  to  the 
ceiling.  Sometimes  they  appear  like  fountains ;  again,  like 
sculptured  monuments ;  but  always  decorated  with  strange 
tracery.  If  we  search  the  cavern,  we  can  find  how  these 
singular  forms  are  made.  Choosing  a  place  where  the  roof 
of  the  cave  is  low,  we  can  see  that  the  water  slowly  trickles 


COURSE   OF   WATER   UNDERGROUND.  79 

through  the  ceiling,  and  falls,  drop  by  drop,  to  the  floor. 
This  water  comes  slowly,  each  drop  glistens  awhile  on  the 
ceiling  before  it  falls ;  during  this  time,  when  it  is  still, 
some  of  the  carbonic  dioxide  gas  escapes  from  it,  and  a 
part  of  the  lime  it  holds  is  laid  down  on  the  ceiling.  We 
can  often  see  the  very  beginnings  of  a  little  hanging  cone 
formed  in  this  way.  Gradually  this  cone  grows  until  it 
hangs  half  way  to  the  floor  of  the  cave.  When  the  drops 
fall,  they  splash  out  and  evaporate  in  the  dry  air  of  the 
cave,  leaving  the  rest  of  their  lime  in  a  little  heap  on  the 
floor.  This  heap  grows  upwards  towards  the  cone  that 
builds  down  from  the  ceiling,  until  at  length  they  are 
united.  Now  the  drops  110  longer  fall,  but  creep  down 
the  sides  of  the  unbroken  column,  evaporating  as  they 
go,  leaving  their  lime  on  its  sides.  And  so  the  mass  of 
stalactites  constantly  grows  larger  and  larger.  In  time 
they  fill  the  whole  gallery ;  and  in  this  way,  after  centu- 
ries, this  passage  of  the  cavern  is  destroyed.  It  is  only 
when  the  ceiling  of  the  cave  is  so  close  that  water  cannot 
trickle  through  it,  that  this  process  does  not  in  course  of 
time  fill  the  whole  space  with  stalactite. 

The  bottom  of  these  caves  can  never  be  lower  than  the 
neighboring  river,  where  the  underground  waters  are  dis- 
charged. As  the  river  cuts  deeper  into  the  rocks  that 
form  its  bed,  the  domes  work  further  down  into  the  rock, 
and  new  and  lower  galleries  are  formed. 

While  this  underground  work  is  going  on,  the  decay  of 
the  surface  is  going  on  also ;  so  that  the  uppermost  galler- 
ies are  slowly  destroyed.  Their  roofs  grow  thin  and  fall 
in,  so  that  they  are  opened  to  the  day.  Now  and  then, 
parts  of  their  ceilings  hold  on  for  a  long  time,  and  in 
this  shape  are  called  natural  bridges.  All  these  natural 
bridges  are  the  remains  of  great  caverns.  Some  of  the 


80  THE   WORK    OF    WATER   ANT)   AIR. 

finest  specimens  known  are  found  in  Carter  County,  Ken- 
tucky, and  Rockbridge  County,  Virginia.  At  this  stage  in 
the  decay  of  a  cavern,  the  ruins  look  like  the  figure. 

This  wearing  down  of  the  caverns  goes  on  for  ages,  so 
that  over  the  place  where  the  caves  now  are  we  may 
believe  there  have  been  many 
other  caves,  perhaps  hun- 
dreds of  feet  in  the  air,  where 
the  earth  once  was,  in  the 
ages  before  the  level  of  the 
ground  was  worn  down  to 
its  present  position. 

To  the  students  of  nature 
these  caverns  are  full  of  in- 
terest. First,  they  show  to 
them  the  wonderful  dissolving 

Fig.  36.    Natural  Bridge.  power    Qf   water  when  it  mns 

through  limestone  rocks.    They  also  contain  many  strange 
forms  of  animal  life.     Some  of  the  outside  animals  use 
these  caves  as  places  of  shelter.     The  bears  that  sleep 
through  the   winter  often  re- 
sort to  caves  for  shelter ;  and, 
during  the  winter  season,  great 
numbers  of  bats  are  found  in 
them.     These   bats  are  often 
to  be  seen  hanging  from  the 
ceilings  in  great  bunches,  one 
grasping  on  the  other,  the  top- 
most holding  to  the  roof.  They 
Fig.  37.    Bats  in  Cave.  are  asleep?  ana  for  all  the  win. 

ter  time  hang  motionless,  as  if  dead.  When  the  spring 
time  comes,  though  the  temperature  of  the  air  does  not 
change  in  the  least,  they  know  in  some  way  that  their 


COURSE   OF   WATER   UNDERGROUND.  81 

time  for  waking  has  come  ;  their  stagnant  blood  begins 
again  to  flow  freely,  the  heat  of  their  bodies  returns, 
and  forth  they  go  to  the  open  air  again. 

Besides  the  many  creatures  that  use  the  caverns  as  a 
place  of  occasional  resort  for  shelter,  there  are  many 
animals  that  live  their  whole  lives  in  this  perpetual  dark- 
ness. There  are  certain  fishes  which  are  found  there  and 
nowhere  else  ;  these  species  have  lost  not  only  their  sight, 
but  the  very  machinery  of  vision.  Their  eyes  have  dis- 
appeared, and  a  very  delicate  sense  of  touch  in  the  parts 
about  the  head  takes  the  place  of  the  sight-sense.  The 
same  thing  occurs  in  many  forms  of  insects  and  crayfishes. 


Fiy.  38.    Cavern  Insects  and  Blind  Fish. 

Their  eyes  also  disappear,  and  their  feelers  become  length- 
ened. These  facts -are  not  only  curious,  but  they  seem 
to  show  the  close  relation  between  the  conditions  in  which 
an  animal  lives  and  the  form  and  functions  of  its  body. 
In  this  age,  when  naturalists  are  trying  to  find  out  the  laws 
that  have  fixed  the  shapes  and  organs  of  living  beings, 
these  facts,  revealed  in  the  underground  world,  are  of  the 
utmost  importance  to  science. 

There  are  many  other  phenomena  connected  with  cav- 
erns. We  can  notice  only  a  few  of  them.  If  on  a  sum- 
mer day  we  approach  the  mouth  of  a  cave  that  opens  low 


82  THE  WORK   OF   WATER   AND   AIR. 

down  on  the  cliffs  near  the  stream,  we  perceive,  even  at 
some  distance  from  the  cavern's  mouth,  a  strong  wind 
that  rushes  out  of  the  shadowy  opening.  This  wind  is 
often  so  strong  that  it  makes  the  ferns  and  bushes  about 
the  mouth  sway  to  and  fro.  It  is  so  cold  that  it  sends  a 
chill  through  us  as  we  step  into  it  from  the  heated  sum- 
mer air.  The  hotter  the  outer  air,  the  stronger  this  blast 
from  the  cavern.  In  the  last  part  of  the  night,  when  the 
outer  air  is  cooler,  the  current  becomes  less  strong.  In  win- 
ter it  turns,  and  we  then  find  a  stream  of  air  entering  the 
cavern,  that  runs  as  briskly  inward  on  cold  days  as  it  did 
outward  in  hot  weather.  From  the  sink  holes  above  the 
cavern,  which  connect  with  the  domes,  we  feel  the  air 
pouring  out  in  a  strong  stream.  When  the  day  is  very 
cold,  we  see  this  warmer  air  of  the  cavern,  which  is  some- 
what moist,  condensed  in  the  cold  outer  air,  so  that  it 
looks  like  steam.  The  reason  for  this  movement  is  plain. 
In  the  summer  time,  the  air  in  the  cavern  is  much  colder 
than  that  in  the  open,  and,  being  colder,  is  much  heavier ; 
it  therefore  flows  out  at  the  lowest  opening  of  the  cave. 
There  is  then  a  current  of  warm  air  setting  down  through 
the  sink  holes  into  the  cavern.  The  cold  rocks  there  soon 
cool  it,  so  that  the  blast  from  the  mouth  of  the  cavern  is 
sustained.  In  the  winter  time,  the  cavern  air  is  much 
warmer,  and  therefore  lighter,  than  the  open  air ;  and  so 
the  cavern  gives  a  current  upward  through  the  sink  holes, 
while  it  draws  in  through  the  mouth.  This  is  the  same 
law  that  rules  the  great  circulation  of  the  air  from  the 
equator  to  the  poles.  So  vast  are  the  interiors  of  these 
greater  caverns,  such  as  the  Mammoth  Cave,  that,  despite 
these  constant  currents  into  it,  the  temperature  constantly 
remains  the  same,  there  hardly  ever  being  a  degree  of 
difference  between  winter  and  summer. 

I 


OOUESZ  OF  WATZB  TTSDEEGBOUXD. 

It  may  be  interesting  to  the  student  to  know  900 
concerning  the  use  of  these  caverns  by  man.  The  Indians 
evidently  travelled  through  most  of  them,  for  we  find  their 
footprints  everywhere.  The  soft  sand  that  fills  many  of  the 
passages  of  these  caves  will  preserve  a  footprint  iimhiujyd 
for  many  centuries,  and  so  we  can  find  the  tracks  of  a 
people  that  vanished  from  this  land  a  century  ago,  the  print 
of  the  moccasin  looking  so  fresh  that  it  might  hare  been 
made  but  an  hour.  We  also  find  there  torches  which 
they  made  by  filling  hollow  canes  with  feiiim,  an  arrange- 
ment that  makes  a  very  good  torch.  It  is  evident  that 
some  of  these  caves  were  used  in  times  of  war  as  places  of 
retreat,  for  some  of  the  remote  chambers,  that  a  stranger 
can  hardly  find  his  way  to,  were  evidently  lived  in  for  a 
considerable  time.  In  one  or  two  cases  the  bodies  of  In- 
dians have  been  found  who  had  evidently  wandered  away, 
while  seeking  to  find  the  way  out,  and  were  lost  in  the 
labyrinth  of  passages.  These  bodies  have  not  decayed. 
but  have  dried  like  mummies  in  the  air.  The  Indians 
also  used  these  caves  as  places  of  buriaL  Sometimes  the 
bodies  were  only  thrown  in  through  the  sink  holes;  in 
this  case  they  were  probably  those  of  enemies  slain  on 
some  battle-field.  At  other  places  we  find  the  bodies 
carefully  buried,  with  all  their  trinkets  and  tools  about 
them,  with  the  hope  that  those  things  might  serve  the  dead 
in  the  long  hereafter  of  plentiful  hunting  and  war  that 
their  friends  hoped  for  them. 

The  white  men,  too.  have  found  use  for  eaves.  For 
many  years  they  were  worked  for  the  saltpetre  with  which 
our  earth  abounds.  A  great  deal  of  the  saltpetre  and  in 
*nrfrr-£  gunpowder  for  the  war  with  Great  Britain,  in 
1312-14,  came  from  the  Kentucky  eaves.  Of  late  yeara 
other  mqujJJBiB  have  taken  its  place,  and  now  the  caverns 


84  THE   WORK  OF  WATER   AND   AIR. 

are  only  a  little  used  for  growing  mushrooms,  and  storing 
various  fruits  and  vegetables  that  keep  better  in  a  uniform, 
rather  dry  air.  This  underground  world  will  remain  of 
use  to  man,  by  giving  him  a  place  in  which  he  can  find  an 
utter  change  from  the  life  of  the  surface ;  a  pure  air,  as 
well  as  a  weird  and  wonderfully  beautiful  scenery. 

European  caves  have  also  been  of  great  use  to  the  geol- 
ogist, from  the  fact  that  in  them  are  preserved  the  remains 
of  many  animals  that  would  otherwise  be  unknown  to  us. 
Many  of  these  caverns  are  very  old.  Some  of  them  have 
been  in  existence  for  the  inconceivable  time  of  a  million  of 
years  or  more.  They  were 
open  in  a  day  when  other 
animals  lived  than  those  now 
upon  the  earth.  Some  of 
these  creatures  used  the  caves 
for  dwellings ;  others  were 
swept  into  them  by  floods, 
or  dragged  in  by  beasts  that 
preyed  upon  them.  These 
remains  have  often  become 
sealed  up  beneath  the  stalac- 
tites that  form  in  the  caves, 
and  so  have  been  well  preserved  from  decay.  By  a  care- 
ful system  of  excavations  it  is  possible  for  the  geologist  to 
get  access  to  these  remains,  and  from  them  to  infer  the 
character  of  the  land  life  in  times  that  would  otherwise  be 
unknown  to  him. 

European  caves  contain  more  bones  than  American, 
because  in  the  old  days  when  they  were  formed  hyenas  and 
jackals  abounded  there.  These  creatures  have  the  habit  of 
dragging  bones  and  dead  bodies  into  caverns ;  and  so  they 
helped  to  stow  away  the  remains  of  many  animals  which 


COURSE   OF    WATER    UNDERGROUND.  85 

have  ceased  to  live,  and  which  would  be  unknown  to  us 
but  for  the  bones  that  are  buried  in  the  caverns. 

Many  of  the  most  ancient  remains  of  man,  which  go  far 
back  beyond  the  time  of  histories,  have  been  found  in  the 
European  caverns,  mingled  with  the  remains  of  animals 
that  exist  no  longer. 

There  are  some  rarer  sorts  of  caves  that  are  not  formed 
in  the  fashion  of  those  in  Kentucky.  These  are  of  three 
classes.  The  first  very  much  resemble  those  of  Kentucky 
in  their  general  character  and  history ;  they  are  cut  out 
of  limestone  by  water,  but  the  water  is  that  of  hot  springs 
and  not  of  the  surface.  This  hot-spring  water,  ascending 
to  the  surface,  may  find  limestone  rocks  in  its  path.  In 
this  case  it  generally  dissolves  out  great  chambers.  Caves 
of  this  character  are  exceedingly  irregular  in  their  form. 
There  are  no  domes,  and,  unlike  surface  caves,  they  may 
be  formed  below  the  level  of  the  river  into  which  their 
waters  discharge.  They  are  not  very  numerous,  but 
exceedingly  interesting  on  account  of  the  valuable  metallic 
deposits  that  they  often  contain.  Some  very  important 
deposits  of  silver  and  gold  ores  occur  in  just  such  caves  as 
these.  The  hot  spring  has  first  carveu  out  the  limestone, 
and  then  filled  its  space  with  ore. 

The  rarest,  yet  sometimes  the  most  curious  caves  of  all, 
are  formed  in  lava  streams.  The  flowing  lava  hardens  on 
the  top,  because  the  air  chills  it,  and  makes  an  arch  over 
the  stream;  then  the  supply  of  melted  rock  failing,  the 
stream  sinks  down  and  leaves  this  arch,  causing  a  cave 
that  reaches  from  the  base  of  the  volcano  to  the  top. 
Such  a  cave  may  be  compared  to  the  arches  formed  over 
temporary  streams  by  the  sharp  cold  of  a  frosty  night 
that  follows  a  winter  thaw.  The  flood  sinks  away,  and 
leaves  the  roof  of  ice  hanging  in  the  air  above  the  course 


86  THE   WORK  OF   WATER    AND   AIR. 

that  the  waters  have  ceased  to  flow  in.  The  next  eruption 
of  the  volcano  is  apt  to  destroy  this  cave ;  but  sometimes 
they  endure  for  ages,  being  deeply  buried  beneath  ashes 
and  other  lavas. 


/'/</.  40.    Lava  Caves  on  a  Volcano. 

We  may  complete  our  account  of  caves  by  a  brief  de- 
scription of  those  made  on  the  sea-shores  by  the  beating  of 
the  waves. 

Wherever  the  coast  is  rocky  and  open  to  the  wide  water, 
the  sea,  in  times  of  storm,  hurls  its  waves  with  great  power 
against  the  shore.  If  these 
waves  held  nothing  but  water, 
they,  despite  the  fury  of  their 
blows,  would  not  be  able  to 
wear  the  hard  rocks  to  any 
great  extent.  But  in  most 
cases  these  waves  havein  their 
grip  pebbles,  or  larger  pieces 
of  stone,  which  they  hurl 
Fly.  41.  Sea  Caves.  against  the  cliffs.  Wherever 

there  is  a  soft  place  in  the  rocks  of  the  cliffs,  the  sea  soon 
makes  a  wedge-shaped  opening;  into  this  opening  the 
stones  torn  from  the  neighboring  shore  are  collected,  so 
that  the  waves  have  a  constant  supply  of  rocky  fragments 


COURSE   OF   WATER   UNDERGROUND. 


87 


with  which  to  batter  the  rocks.  In  this  way  they  some- 
times cut  channels  extending  some  hundreds  of  feet  back 
from  the  sea  front. 

When  the  rocks  of  the  shore  have  dykes  or  veins  in 
them,  these  deposits  are  often  softer  than  the  rocks  on 
which  they  lie,  and  so  are  excavated  by  the  sea.  All 
along  the  shores  of  New  England  we  find  many  of  these 
furrows,  commonly  called  chasms.  When  the  sea-waves 
rash  freely  into  these  furrows,  their  spray  is  sometimes 
during  storms  forced  high  into  the  air,  when  the  crevice 
is  commonly  called  a  spouting  horn. 

These  caves  worn  by  the  sea  are  never  very  large,  and 
have  none  of  the  beauty  or  interest  that  belongs  to  those 
made  in  limestone  rocks  by  the  waters  of  the  land. 


View  in  Luray  Cave. 


CHAPTER  IV. 


THE  DEPTHS   OF  THE  EARTH, 


LESSON    I. 

VOLCANOES. 

TTTE  should  always  bear  in  mind  how  small  a  part  of 
*•  the  whole  earth  is  really  known,  or  we  can  know 
anything  about.  Our  deepest  mines  have  never  gone 
more  than  one  seven-thousandth  part  of  the  way  from  the 
surface  to  the  centre.  The  upturned  edges  of  stratified 
rocks  make  it  possible  for  us  to  see  somewhat  further  into 


Fig.  42.    Showing  how  Rocks  are  exposed  by  Tilting. 

conditions  of  the  interior,  for  they  sometimes  show  us  rocks 
that  have  been  buried  twenty  thousand  feet  or  more  under 
the  earth,  and  have  since  been  exposed  to  the  light  of 
day  by  the  squeezing  and  tearing  that  happens  in  moun- 
tain building ;  yet,  with  this  help,  we  can  never  see  in  their 
natural  state  rocks  that  have  been  more  than  one  five- 


VOLCANOES.  89 

hundredth  of  the  distance  down  to  the  earth's  centre.  In 
the  diagram,  such  tilted  rocks  are  shown. 

The  only  way  in  which  we  can  form  any  notion  of  what 
goes  on  at  greater  depths,  is  through  volcanoes ;  they,  there- 
fore, deserve  the  careful  study  of  every  one  who  wishes  to 
know  the  little  that  can  be  learned  of  the  vast  unknown 
region  of  the  earth's  interior. 

Let  us  first  see  what  volcanoes  are,  in  order  that  we  may 
learn  what  they  can  teach  us  of  this  inner  mass  of  the 
earth. 


Fill.  43.    Vesuvius  in  Eruption. 

A  volcano  is  an  opening  in  the  crust  of  the  earth  through 
which  molten  rock  or  lava  and  other  stones,  along  with 
great  quantities  of  steam,  are  thrown  out  with  great  vio- 
lence into  the  air.  This  steam  is  heated  far  above  the 
boiling  point  of  water ;  up,  indeed,  to  the  melting  point 
of  rock,  and  escapes  with  such  force  that  it  drives  the 
rocks  before  it,  as  by  an  explosion  of  gunpowder.  Some- 
times these  pieces  of  rock  are  so  pulverized  that  they  are  but 
dust,  that  floats  away  in  the  form  of  a  cloud,  and  has  been 
known  to  drift  more  than  a  thousand  miles  before  it  falls  to 
earth ;  but  the  most  of  this  rock  falls  near  the  mouth,  and 


90  THE  DEPTHS  OF  THE  EARTH. 

makes  a  hill  called  the  volcanic  cone.  It  often  but  not 
always  happens  that  the  heat  of  these  gases  is  so  intense 
and  long-continued,  that  the  rocks  through  which  the  gas 
forces  its  way  become  melted,  and  flow  out  of  the  cone  in 
the  form  of  lava.  But  the  amount  of  this  lava  is  gener- 
ally small  compared  with  the  cinders  and  ashes,  and  very 
small  indeed  compared  with  the  escaping  steam,  which  is 
the  principal  feature  in  all  volcanic  eruptions. 

Volcanoes  are  never  found  in  the  middle  of  the  conti- 
nents, but  only  near  the  sea-shore,  and  over  the  bottom 
of  the  greater  seas  and  oceans.  Whenever  we  find  old 
volcanoes  in  the  middle  of  the  lands,  we  find  them  no 
longer  active,  and  we  can  prove  that  when  they  were 
active  the  sea  lay  near  their  bases. 

This  shows  us  that  volcanoes  are  in  some  way  connec- 
ted with  the  processes  that  go  on  under  the  sea.  There 
have  been  a  great  many  theories  to  account  for  this  rela- 
tion between  volcanoes  and  the  sea ;  some  have  supposed 
that  the  sea-water  found  its  way  down  through  crevices 
to  the  central  hot  part  of  the  earth,  and  was  there  changed 
into  steam  which  poured  out  through  the  volcanoes ;  but 
we  readily  see  it  would  be  easier  for  the  steam  to  come 
out  of  the  passage  through  which  the  water  went  in  to 
the  heated  region,  than  for.  it  to  force  a  new  way  to  the 
surface,  so  we  must  give  up  this  idea.  The  most  reason- 
able view  is,  that  the  volcanoes  are  outbreaks  of  the  steam 
that  is  confined  in  the  rocks  beneath  the  sea  or  near  to  it. 
A  certain  amount  of  water  is  fixed  in  the  rocks  when 
they  are  formed  on  the  sea-floor.  All  our  rocks  made  in 
water  have  from  four  to  fifteen  per  cent  of  their  mass 
made  up  of  imprisoned  water.  This  water  becomes  heated 
because  the  beds  laid  down  on  top  of  it  are  very  thick, 
and  act  like  a  blanket  to  keep  the  earth's  heat  in.  In  the 


VOLCANOES. 


91 


course  of  ages  this  water  may  come  to  have  a  heat  as  great 
as  that  of  melted  iron.  Now,  if  any  crack  is  found  in  the 
overlying  beds  that  will  let  these  gases  escape,  we  shall 
have  a  volcano.  This  will  account  for  the  fact  that  vol- 
canoes are  jets  of  very  hot  steam,  and  that  they  always  lie 
near  the  sea-shore  or  on  its  bottom. 

The  reason  why  volcanoes  do  not  occur  far  away  from 
sea-floors  is  probably  because  it  is  only  on  these  parts  of 
the  surface  that  the  great  blankets  of  rock  are  laid  down 
on  the  earth. 

We  can  help  ourselves  to  figure  this  effect  of  beds  of 
rock  in  raising  the  heat  of  rocks  below  them,  if  we  re- 
member that  over  all  the 
earth's  surface  a  constant  flow 
of  heat  is  streaming  out 
through  the  earth  and  going 
away  among  the  stars.  Enough 
of  this  heat  escapes  each  year, 
from  every  square  mile  of 
the  earth's  surface,  to  boil 
a  great  many  barrels  of  water. 
If  the  reader  could  heap  any 
kind  of  rocks  on  the  ground 
where  he  stands,  so  that  the  Fig.^.  Rise  of  Heat  in  Rocks, 
surface  would  be  covered  to  the  depth  of  two  miles,  the 
water  in  the  soil  would,  on  account  of  this  blanket  of  rock, 
rise  slowly  to  a  greater  heat  than  that  of  boiling  water. 

Most  volcanoes  are  found  in  places  where  civilized  men 
have  not  had  a  chance  to  watch  them  for  a  very  long 
while.  The  history  of  only  three  is  known  for  as  many 
as  one  thousand  years.  These  are  Vesuvius  and  ^tna  in 
Italy,  and  Skaptar  Jokul  in  Iceland.  Of  Vesuvius  and 
we  have  some  account  for  more  than  two  thousand 


92  THE  DEPTHS  OF  THE  EARTH. 

years.  These  histories  show  us  that  volcanoes  are  not  com- 
monly in  a  state  of  activity.  More  than  half  their  life  is 
spent  in  a  state  of  repose,  their  powers  slumbering  below 
the  earth.  Sometimes  these  still  times  continue  for  sev- 
eral hundred  years.  Vesuvius  was  not  even  known  to  be 
a  volcano  until  the  year  79,  though  the  region  about  it 
had  been  dwelt  in  by  the  Greeks  and  Romans  for  at  least 
four  hundred  years  before  that  time.  It  was  covered 
with  forests  and  tilled  fields.  At  that  day  men  had  not 
studied  the  forms  of  its  surface,  else  they  would  have 
known  that  its  cup-like  shape,  and  the  nature  of  the  ashes 
that  made  up  the  mountain,  marked  it  as  a  volcano. 
Seventy-nine  years  after  Christ's  birth,  the  silent  moun- 
tain stood  amid  one  of  the  most  fertile  and  thickly 
peopled  parts  of  the  earth.  It  was  the  richest  part  of  the 
Roman  Empire  in  its  most  prosperous  days.  Early  in  that 
year  there  began  to  be  earthquakes  in  the  region  about  it. 
Still,  though  there  were  volcanoes  on  the  island  of  Ischia, 
which  lies  within  sight  of  Vesuvius,  that  had  proved 
very  destructive  to  life  and  property,  no  one  thought  of 
the  danger  of  an  explosion  from  the  long  silent  Vesuvius. 
Finally,  a  most  frightful  explosion  took  place.  The  upper 
part  of  the  mountain  was  blown  to  pieces,  and  the  coun- 
try for  many  miles  about  was  rained  on  for  days  by  stones 
and  ashes,  falling  so  thickly  that  a  perfect  darkness  was 
made.  Men  and  beasts  were  killed,  even  a  dozen  miles 
away,  by  the  shower  of  hot  stones,  and  all  this  beautiful 
country  was  reduced  to  ruin.  The  famous  Roman  natu- 
ralist, Pliny  the  elder,  who  was  admiral  of  a  fleet  sta- 
tioned at  Misenum  in  that  district,  a  town  about  twenty 
miles  from  the  mountain,  lost  his  life  at  a  point  over  a 
dozen  miles  away  from  the  volcano,  having  been  suffo- 
cated by  the  vapors  of  the  eruption  in  his  effort  to  save 


VOLCANOES.  93 

the  inhabitants  of  the  shore.  So  severe  was  the  shower 
of  ashes,  that  his  attendants  could  not  bear  his  body 
away  from  the  place  where  he  had  met  his  death. 

At  least  two  large  and  wealthy  cities,  Herculaneum 
and  Pompeii,  were  buried  beneath  the  prodigious  masses 
of  ashes  or  small  stones  that  were  thrown  out  from  the 
volcano,  or  overwhelmed  in  the  mud  made  by  the  heavy 
rains,  which  always  come  with  a  great  eruption.  There 
were  doubtless  many  small  villages  overwhelmed  at  the 
same  time,  the  names  of  which  are  unknown  to  us,  for  it 
is  only  by  chance  that  we  learned  of  the  destruction  that 
came  upon  Herculaneum  and  Pompeii.  The  accounts 
written  at  the  time  simply  say  that  many  places  were  de- 
stroyed. 

After  this  eruption,  others  came  at  long  intervals, 
sometimes  over  a  hundred  years  going  by  without  the 
least  sign  of  activity  in  the  mountain,  so  that  a  good 
part  became  covered  with  vineyards  and  gardens.  Then, 
with  a  period  of  earthquakes  that  set  all  the  mountain 
to  trembling,  the  volcano  would  again  burst  forth.  It 
was  not  until  after  it  had  been  active  for  about  a  thou- 
sand years  that  it  began  to  throw  out  lava.  Lava  erup- 
tions have  been  growing  steadily  more  common  than  of 
old,  and  the  eruptions  have  been  growing  more  frequent 
and  less  violent.  For,  as  a  general  rule  with  volcanoes, 
where  their  eruptions  come  only  at  long  intervals,  they 
are  much  more  violent  than  they  are  when  they  quickly 
follow  each  other.  A  little  volcano,  called  Stromboli, 
which  lies  between  Vesuvius  and  JEtna,  has  been  in  con- 
stant eruption  for  centuries,  scarcely  a  day  passing  when 
it  does  not  throw  out  some  fiery  gas  and  melted  stones ; 
but  its  eruptions  are  never  very  violent.  It  is  to  be 
noticed  that  the  larger  the  volcano,  the  more  likely  it  is 


94  THE  DEPTHS  OF  THE  EARTH. 

to  throw  out  lava.  ^Etna  has  had  many  worse  lava  flows 
than  Vesuvius,  and  is  one  of  the  best  places  to  study 
such  streams. 

When  lava  escapes  from  a  volcano,  it  is  generally  very 
fluid.  Sometimes  it  appears  almost  as  liquid  as  water, 
though  it  really  is  more  like  melted  lead  or  quicksilver, 
which  are  less  fluid  than  water,  though  they  flow  with  ease. 
The  lava  generally  flows  very  quickly  when  it  escapes 
from  the  crater ;  but  it  soon  begins  to  cool,  and  forms  a 
solid  crust  upon  its  surface  that  makes  it  hard  for  it  to 
creep  along.  Finally,  it  crawls  so  slowly,  pushing  along  a 
mass  of  broken  solid  lava  in  front  of  it,  that  it  looks  like 
a  large  heap  of  rolling  stones;  yet  the  lava  within  the 
stream  stays  fluid,  and  for  months  it  may  crawl  along  in 
this  fashion,  making  only  a,  few  hundred  feet  of  advance 
in  a  day.  Still  it  is  strong  enough  to  overwhelm  towns 
and  destroy  fields  in  its  course.  Sometimes  the  hard  coat- 
ing of  frozen  lava  will  break  open  and  let  the  fluid  inte- 
rior out  in  a  fresh  stream,  which  in  time  becomes  clogged 
in  the  same  way.  It  often  happens  that  these  lava 
streams  fall  into  the  valleys  of  rivers.  It  then  drives  the 
water  into  steam,  and  effaces  the  course  of  the  river. 
After  the  lava  has  cooled,  the  river  commonly  cuts  itself 
a  new  bed  alongside  of  the  lava ;  often  there  is  a  stream 
on  either  side  of  the  lava,  and  in  time  these  wear  down  so 
deep  that  the  lava  is  left  on  a  hill-top.  This  has  often 
occurred  in  California,  where  volcanoes,  now  extinct, 
once  filled  to  the  very  brim  with  lava  the  valleys  that  lead 
from  the  Sierra  Nevada.  We  know  much  of  these  old 
Californian  streams,  for  their  beds  contain  gold  among  the 
gravel,  and  a  good  deal  of  mining  is  carried  on  in  their 
ancient  beds.  In  the  figure  No.  45,  the  dotted  line  shows 
the  position  of  the  old  valley  which  has  been  filled  with 


VOLCANOES. 


95 


lava,  while  below  we  see  the  present  valleys.  The  old 
river  bed,  containing  gold,  lies  under  the  lava  stream, 
which  now  caps  a  hill. 

Although  volcanoes  rarely  give  out  large  amounts  of 
lava,  there  are  some  places  in  the  world  where  there  are 
very  large  regions  that  have  been  covered  with  these 
floods  of  molten  rock.  One  of  these  in  California,  Oregon, 
and  Washington  Territory,  is  nearly  as  large  as  France. 

Although  volcanoes  are  among  the  most  violent  and 
seemingly  disordered  of  the  earth's  works,  they  play  a 
definite  and  bountiful  part  in  its  machinery.  If  the  world 


Old  River  Beds  filled  with  Lava. 

were  without  them,  it  is  hard  to  see  how  life  could  long 
exist.  This  seems  a  paradox,  but  its  truth  is  easily  made 
plain.  We  have  seen  that  the  plants  of  the  earth  live  by 
taking  the  carbonic  dioxide  from  the  air.  In  an  atmos- 
phere without  this  gaseous  carbon  plants  could  not 
grow ;  and,  as  animals  depend  on  plants  for  their  food, 
they,  too,  have  the  liveliest  interest  in  this  element  in 
the  air.  The  amount  of  this  carbon  is  never  large,  not 
exceeding  one  three-hundredth  of  its  bulk.  If  there  were 
not  means  whereby  this  carbon  could  come  back  to  the  air, 
it  would  require  only  a  few  centuries  to  make  the  supply 
so  small  that  plants  could  not  grow.  A  great  deal  of  the 


yt>  THE  DEPTHS  OF  THE  EARTH. 

carbonic  dioxide,  perhaps  nine-tenths,  that  goes  into  the 
plant,  comes  back  to  the  air  in  their  decay;  but  every 
bit  of  coal  that  is  formed,  every  grain  of  limestone  that 
is  deposited  on  the  sea-floor,  takes  so  much  carbon  from 
the  air  and  lays  it  away  in  the  rocks  ;  so  that  it  is  certain 
that  the  vegetable  world  could  not  long  endure  without 
some  renewal  of  the  carbon  supply  in  the  air.  The  prin- 
cipal way  in  which  this  buried  carbon  can  get  back  to  the 
air  is  through  the  gases  that  volcanoes  throw  out  in  their 
times  of  eruption.  Although  the  most  of  this  gas  they 
pour  forth  is  water  in  the  state  of  steam,  there  is  a  con- 
siderable amount  of  carbonic  acid  gas  thrown  out  in  every 
eruption.  Sometimes  so  great  is  the  quantity  that  it  suf- 
focates the  animals  for  some  miles  distant  about  the  crater. 
We  do  not  notice  it  much  in  an  ordinary  eruption,  for  the 
reason  that  the  gas  is  taken  into  the  water  and  steam,  and 
so  locked  up  there  that  it  does  not  aifect  life ;  but  in  an 
eruption  of  Vesuvius  or  JEtna  there  is  as  much  of  this  gas 
of  carbon  given  forth  to  the  air  as  would  be  taken  from 
it  by  the  burial  of  a  large  amount  of  coal  or  limestone. 
As  volcanoes  are  continually  in  eruption  in  one  part  of 
the  earth  or  another,  it  follows  that  they  play  a  most  nec- 
essary part  in  keeping  the  world  fit  for  life;  and  the 
destruction  they  do  is  of  trifling  importance  compared 
with  the  benefits  they  confer.  This  adds  another  to  the 
many  proofs  that  this  earth  is  wonderfully  arranged  for 
the  uses  of  living  beings.  *We  have  seen  that  the  orderly 
work  of  the  air  and  the  waters,  in  all  their  manifold  actions, 
seem  to  foster  this  life ;  but  even  the  most  violent  and 
seemingly  destructive  actions  of  volcanoes  also  aid  in 
making  the  conditions  that  life  requires.  When  we  look 
at  the  buried  cities  of  Pompeii  and  Herculaneum,  or 
behold  the  ravaged  vineyards  and  olive  orchards  about 


VOLCANOES. 


97 


Vesuvius,  we  may  set  against  this  account  of  ill  the  fact 
that  in  every  eruption  of  Vesuvius  there  comes  forth  the 
carbon  that  is  to  find  its  place  in  the  life  of  the  whole 
world ;  so  that  the  damage  it  brings  about  is  trifling  com- 
pared with  the  benefits  it  confers. 


Last  Stages  of  a  great  Eruption  of  Vesuvius,  from  a  photograph. 


98  CURRENTS   OF   AIR   AND   SEA. 

LESSON  II. 
ON  THE  CURRENTS  OF  AIR  AND  SEA. 

WE  have  already  spoken  of  the  atmosphere  in  a  preceding 
chapter.  We  will  now  look  more  closely  into  the  work 
that  comes  from  the  action  of  its  currents,  the  winds. 

The  life  of  our  earth  is  of  two  kinds :  the  life  of  anima- 
ted nature,  and  the  life  of  the  inanimate  world,  shown  in 
the  movements  of  the  air  and  water,  and  the  other  motions, 
such  as  those  of  volcanoes.  Except  the  disturbances  that 
come  from  beneath  the  earth,  all  its  motions  are  derived 
from  the  sun's  heat;  all  the  life  of  animals  and  plants,  all 
the  currents  of  the  air,  the  rivers,  and  the  oceans,  every 
stir  of  its  surface,  is  due  to  the  force  that  comes  from  the 
sun  and  stars.  The  motions  of  our  own  limbs,  even  the 
beating  of  our  hearts,  are  only  forms  of  force  that  come 
to  the  earth  from  the  great  sources  of  power,  the  sun  and 
the  fixed  stars.  The  sun's  heat  causes  the  plants  to  grow ; 
and  it  is  this  solar  force  that  comes  to  us  in  our  food, 
and  is  the  support  of  all  animal  bodies.  Every  wind 
that  blows,  every  stream  that  runs,  on  land  or  in  the 
sea,  moves  because  impelled  by  this  power  from  beyond 
the  earth.  If  our  earth  could  be  cut  off  from  these 
sources  of  power,  all  its  life  would  soon  become  stilled. 
One  night,  of  a  few  months'  duration,  would  bring  its 
whole  surface  to  a  cold  of  more  than  one  hundred  degrees 
below  zero  of  Fahrenheit,  and  all  the  animate  and  inani- 
mate life  would  be  stilled;  the  seas  and  rivers  would 
change  to  motionless  ice,  and,  until  the  day  came  again, 
no  motions,  save  those  of  the  earthquake  and  the  volcano, 
would  occur  upon  the  earth. 


CURRENTS   OF   AIR   AND   SEA. 

Since  this  world  is  moved  by  the  force  that  comes  from 
the  sun,  we  should  get  some  idea  of  the  way  in  which  this 
heat  comes  to  us,  and  the  mode  in  which  it  works  after  it 
has  arrived  on  the  earth. 

This  solar  force  comes  to  the  earth  in  the  form  of  heat 
and  light.  Both  the  heat  and  light  are  necessary  for  the 
machinery  of  animal  and  vegetable  bodies,  but  the  move- 
ments of  the  winds,  the  waves,  and  the  currents  of  the 
sea  require  only  the  heat  for  their  action.  The  supply  of 
light  and  heat  comes  to  the  earth  from  two  different 
sources.  Somewhere  near  one-half  the  heat  comes  from 
the  fixed  stars.  This  heat  from  the  far-away  stars  descends 
equally  on  all  parts  of  the  earth's  surface ;  but,  if  it  alone 
came  to  the  earth,  there  would  still  be  no  movement  for 
it ;  the  oceans  would  be  frozen  to  their  bottoms,  and  life 
of  all  kinds  would  be  impossible.  All  that  this  star  heat 
does  is  to  lift  the  general  temperature  of  the  earth's  sur- 
face from  a  far  greater  cold  to  an  average  temperature  of 
about  one  hundred  degrees  below  zero  of  Fahrenheit. 
Although  this  seems  but  a  poor  gift,  it  is  still  of  priceless 
value,  as  it  makes  it  possible  for  the  sun  to  do  its  good 
work  of  quickening  life  on  the  earth;  but  for  this  help 
from  the  stars,  the  sun  could  not  accomplish  this  task ; 
it  alone  would  have  too  much  work  to  do. 

The  sun  gives  us  both  light  and  heat ;  but,  in  place  of 
giving  it  as  the  stars  give  their  heat,  equally  over  all  the 
surface,  it  pours  a  great  amount  of  this  light  and  heat 
upon  the  regions  between  the  tropics,  and  gives  much  less 
to  the  regions  about  the  poles.  If  this  heat  stayed  where 
it  fell,  or  if,  like  the  light,  it  were  a  momentary  thing, 
disappearing  as  soon  as  the  earth  turned  its  face  away 
from  the  sun  in  the  night  time,  then  the  world  would  fare 
badly ;  for,  during  the  mid-day  at  the  tropics,  the  heat 


100  CURRENTS   OF  AIR   AND   SEA. 

would  be  too  great  for  life  to  endure,  and  in  the  night 
everything  would  perish  in  a  frost  of  more  than  a  hundred 
degrees  below  zero. 

Fortunately  heat  can  be  stored  up,  as  light  cannot  be. 
The  rocks  and  the  air  can  take  in  some  of  it,  and  the 
water  can  take  in  a  very  large  quantity.  This  heat  is 
given  out  again,  after  having  been  stored  away  for  a 
time.  Thus,  when  the  night  comes,  in  place  of  the  ther- 
mometer falling  to  one  hundred  degrees  below  zero  at 
dawn  on  a  summer's  night  in  the  tropics,  it  rarely  goes 
below  sixty  above  zero ;  because  these  things  which  have 
been  taking  up  heat  all  day  proceed  to  give  it  out  in 
steady  streams.  So,  too,  in  the  winter,  the  earth  and  seas 
slowly  yield  up  the  heat  the  summer  gave  them  to  moder- 
ate the  rigors  of  the  cold  seasons.  Thus  it  happens,  that 
islands,  even  in  seas  near  the  poles,  have  often  a  some- 
what uniform  climate  in  winter  and  summer.  The  aver- 
age difference  of  temperature  of  the  months  in  Cornwall  in 
southern  England  is  not  more  than  thirty  degrees  in  any 
one  year.  But  the  most  important  effect  of  this  great  heat- 
storing  ability  of  water  is  found  in  the  power  it  has  of 
carrying  heat  from  the  equatorial  regions  to  the  poles. 
This  it  does  in  the  way  we  shall  soon  consider.  If  we 
watch  a  heated  stove  in  the  middle  of  a  large  room,  the 
walls  of  which  are  cooled  by  the  outside  winter  air,  we 
easily  see,  by  the  aid  of  a  little  smoke  in  the  room,  that 
the  air  rises  over  the  stove  to  the  ceiling,  floats  off  to  the 
sides  of  the  room,  falls  down  there  to  the  floor,  and  then 
runs  along  it  to  the  stove,  making  a  continuous  round. 
This  is  because  heated  air  is  much  expanded,  and,  there- 
fore, greatly  lighter  than  the  cold.  We  may  illustrate 
this  by  means  of  a  paper  balloon,  with  an  open  mouth 
below,  underneath  which  a  small  piece  of  sponge  dipped 


CTJEEENTS    OF   THE    AIR   AND    SEA.  101 

in  turpentine  or  alcohol  is  hung.  This  sponge  being  fired, 
the  heated  air  will  swell  the  balloon,  and  lift  it  far  above 
the  earth.  The  first  balloons  ever  used  to  lift  men  into 
the  air  were  of  this  nature. 

The  circulation  of  the  air  about  the  stove  is  exactly 
parallelled  by  the  circulation  of  the  air  on  the  earth. 
The  region  between  the  tropics  is  so  hot  that  the  air  is 
impelled  to  rise ;  to  fill  the  vacant  space,  the  air  rushes 
in  from  the  regions  to  the  north  and  south  in  the  strong 
gale  we  call  the  trade  winds.  The  upper  air  streams  off 
towards  the  poles  in  a  mighty  flood  as  wide  as  the  seas ; 


/'«//.  4G.    Diagram  of  Air  Curreuts. 

on  the  high  mountains  near  the  tropics  we  may  feel  it 
always  blowing  a  steady  gale,  never  ceasing  by  day  or 
night  for  ages. 

If  the  earth  stood  still  on  its  axis,  these  winds  would 
come  straight  down  the  surface  of  the  earth  towards  the 
equator  following  the  meridians ;  but,  because  the  earth 
spins  around  on  the  polar  axis  from  west  to  east,  they  come 
slantingly  down  upon  the  equator  from  the  north-east  and 
the  south-east.  It  is  a  little  difficult  to  give  a  simple  and 
clear  explanation  of  this  slanting  course  of  the  winds  that 
blow  towards  the  equator.  It  may  best  be  understood  by 
spinning  a  round,  flat  piece  of  cardboard  on  a  central 


102  CURRENTS   OF   THE  AIR   AND   SEA. 

point,  and  trying  to  roll  a  marble  from  the  centre  to  the 
outer  edge.  It  will  be  found  that  the  marble  will  not  roll 
along  the  short,  straight  line  from  the  centre  to  the  cir- 
cumference, but  will  follow  a  curved  line,  coming  to  the 
edge  as  shown  in  the  figure.  This  is  because  the  marble 
has  in  its  course  always  a  less  rate  of  spinning  than  the 
card  over  which  it  is  travelling.  The  friction  on  the  card 
makes  it  spin  around  with  it ;  but  it  comes  to  each  part  on 
its  course  at  the  rate  of  the  part  which  it  has  just  left.  A 
particle  of  air,  when  it  starts  in  the  trade  winds  on  ite 
journey  to  the  equator,  is  spinning  round  with  the  world 
on  which  it  lies  at  the  rate  of 
about  five  hundred  miles  an 
hour;  when  it  gets  to  the 
equator,  it  must  travel  a  thou- 
sand miles  an  hour.  The 
result  is  that  it  lags  behind 
at  every  stage  of  the  journey, 
just  as  the  marble  does,  and 
so  comes  obliquely  from  the 
Fig.  47.  Deflection  of  Air  Currents,  north-east  and  south-east,  and 
not  squarely  down  upon  the  equator.  All  this  has  a  great 
importance,  as  we  shall  now  see. 

These  trade  winds  blow  strongly,  so  that  they  send  a 
ship  at  great  speed,  and,  as  may  be  imagined,  they  sweep 
the  surface  water  of  the  sea  along  with  them  at  the  rate 
of  two  or  three  miles  an  hour.  This  water  flows  in  the 
same  direction  as  the  wind ;  and  so,  as  there  are  two  streams 
of  water,  one  from  the  south-east  and  one  from  the  north- 
east, each  as  wide  as  the  ocean  in  which  they  lie,  the  two 
pressing  against  each  other  at  the  equator  make  a  current 
two  or  three  hundred  miles  wide,  flowing  towards  the 
west  at  the  rate  of  several  miles  an  hour,  or  about  as  swift 


CURRENTS    OF    THE   AIR   AND    SEA.  103 

as  a  large  river.  This  water  is  very  warm,  from  the  heat 
given  it  by  a  tropical,  overhead  sun ;  so  it  is  a  vast  hot 
stream  carrying  perhaps  more  water  than  all  the  rivers  of 
the  world. 

If  there  were  no  lands  in  the  tropics,  this  river  of  the 
sea  would  flow  around  the  earth  as  a  great  girdle  of  run- 
ning water ;  but  when  it  strikes  against  the  shores,  it  is 
split  in  two,  and  runs  as  two  streams  towards  either  pole. 
There  are  two  of  these  streams  in  the  Atlantic  and  two  in 
the  Pacific  Ocean  ;  in  the  Indian  Ocean,  because  there  is 
30  much  land  near  by  in  the  northward,  the  trade  winds 
are  not  steady  enough  to  make  any  very  distinct  current. 
We  know  only  one  of  these  streams  at  all  well.  This  is 
that  known  as  the  Gulf  Stream,  because  a  part  of  its 
water  comes  out  of  the  Gulf  of  Mexico,  into  which  it  flows 
from  the  Caribbean  Sea.  This  stream  flows  into  the  north 
Atlantic.  When  it  starts  from  the  West  Indian  Islands, 
it  is  a  stream  about  one  hundred  miles  wide  and  several 
hundred  feet  deep,  flowing  at  the  rate  of  four  miles  an 
hour.  As  it  gets  northward  it  widens  and  becomes  more 
shallow,  and  steadily  sinks  in  temperature.  As  far  north 
as  England  it  has  a  ver}^  gentle  current,  but  is  still  much 
warmer  than  the  air  usually  is. 

As  it  goes  northward,  this  stream  leaves  the  American 
shore  which  turned  it  northwards,  and  moves  to  the  east- 
ward, crossing  the  Atlantic.  If  the  reader  has  seen  why 
the  air  currents  turned  to  the  west  in  going  southward,  in 
the  trade  winds,  it  will  now  be  easy  to  understand  why 
the  current  of  the  sea  strikes  off  to  the  east  in  going 
northward.  Each  particle  of  water,  when  it  leaves  Flor- 
ida, is  moving  to  the  east,  in  the  spinning  of  the  earth 
on  its  axis  at  the  rate  of  several  hundred  miles  an 
hour.  As  it  goes  towards  the  pole  it  is  constantly  coming 


104  CURRENTS   OF   THE   AIR   AND    SEA. 

into  regions  which  have  a  less  movement  to  the  east,  so 
its  momentum  causes  it  to  outrun  the  easterly  motion  of 
the  earth  at  these  points,  and  to  swing  off  to  the  east  or 
the  direction  in  which  the  earth  is  turning. 

These  waters  that  seek  the  pole  return  southwards  in 
the  depths  of  the  sea  in  southward-setting  currents  that 
move  slowly  along  the  bottom,  or  creep  along  the  western 
shores  of  the  oceans.  So  the  waters  of  the  seas  are  con- 
stantly sent  towards  the  poles  in  warm  currents,  and 
returned  in  cold  streams  to  the  tropics,  to  be  again  charged 
with  the  life-giving  heat  and  sent  again  to  high  latitudes. 

If  the  heat  of  the  water  stayed  where  it  fell,  then  the 
tropics  would  be  too  hot  for  life ;  while,  all  about  the  poles, 
even  as  far  south  as  New  England,  the  ocean  would  be 
frozen  so  there  would  be  only  a  little  strip  of  the  earth  in 
either  hemisphere  fit  for  life.  But,  by  this  machinery  of 
the  moving  waters,  the  temperature  of  the  earth  is  so  bal- 
anced that  but  little  of  it  is  not  suited  to  some  forms  of 
animals  and  plants.  We  get  an  idea  of  the  power  of 
these  ocean  currents  when  we  know  that  the  Gulf  Stream 
sends  as  much  heat  to  the  region  within  the  Arctic  circle 
as  comes  upon  that  part  of  the  earth  from  the  sun. 

Now,  heat  not  only  affords  the  possibility  of  life,  but  it 
is  the  power  that  sets  all  of  its  machinery  in  motion ;  so 
it  happens  that  this  machinery  of  the  winds  serves  to  dis- 
tribute the  source  of  life  over  the  .earth,  equalizing  it  so 
that  the  whole  of  the  earth's  seas  and  lands  give  some 
chance  to  living  beings. 

The  winds  alone  cannot  do  this  work  of  distributing 
the  earth's  heat,  for  the  air  cannot  hold  much  heat  stored 
in  its  particles.  If  it  were  not  for  the  currents  of  the  sea, 
there  would  be  no  chance  of  having  enough  heat  carried 
to  the  regions  about  the  poles  to  keep  them  from  perpet- 


CURRENTS   OF  THE  AIR  AND  SEA.  105 

ual  frost,  or  enough  taken  away  from  the  tropics  to  keep 
their  lands  and  seas  from  becoming  so  hot  that  few  living 
things  could  endure  the  climate.  But,  in  a  smaller  and 
local  way,  the  winds  do  a  great  deal  of  work.  They 
carry  the  warmth  and  moisture  from  the  seas  into  the 
lands,  giving  them  their  needed  quantities  of  these  all- 
important  things. 

It  is  easy  to  see  that  the  shape  of  the  lands  fixes  the 
course  of  these  ocean  streams.  The  great  Gulf  Stream, 
that  flows  into  the  north  Atlantic,  finds  an  open  passage- 
way far  to  the  north ;  on  the  other  hand,  the  great  stream 
of  the  Pacific,  the  Japan  Current,  is  shut  out  from  tbe 
Arctic  Sea  by  the  peninsulas  of  Alaska  and  eastern  Asia, 
so  that  it  cannot  pour  in  its  warm  waters  to  relieve  the 
cold  about  the  poles.  If  these  lands  should  sink  down 
beneath  the  sea,  as  the  lands  often  do,  letting  the  Pacific 
stream  into  the  Arctic  Ocean,  the  result  would  be  that  the 
tropics  would  become  cooler,  and  the  northern  regions  a 
good  deal  warmer  than  they  are  at  present.  Many  of  the 
wonderful  changes  of  climate  that  we  know  to  have  oc- 
curred in  the  past  are  probably  to  be  explained  by  such 
change  in  the  direction  in  which  the  ocean  currents  flow. 
When  they  can  reach  the  poles  in  strong  streams,  the 
tropics  become  cooled  by  the  heat  that  the  waters  bear 
away  from  them,  and  the  regions  around  the  poles  warmed 
by  their  waters.  When  the  lands  force  the  ocean  cur- 
rents from  the  poles,  the  tropics  become  hotter,  and  the 
lands  and  seas  of  high  latitudes  are  given  over  to  intense, 
life-destroying  cold. 

There  are  probably  many  other  causes  of  climatic 
changes  in  the  earth's  surface.  The  sun's  heat  may  vary, 
or  the  changes  in  the  earth's  path  about  it  may  alter  so 
that  the  winter  and  summer  seasons  in  any  country  are 


106 


CURRENTS   OF   THE  AIR   AND  SEA. 


sometimes  of  nearly  the  same  temperature,  and  again, 
more  different  than  they  now  are.  But  this  change  in  the 
course  of  the  ocean  streams,  depending  on  alterations  in 
the  position  of  the  ocean  currents,  is  probably  the  princi- 
pal cause  of  the  great  climatic  changes  in  the  past  history 
of  the  earth.  We  know  that  the  course  of  these  streams 
depends  on  the  shape  of  the  lands  ;  we  know,  also,  that 
the  lands  are  constantly  changing  their  shapes ;  so  it  fol- 
lows that,  as  the  distribution  of  the  heat  on  the  earth's 
surface  depends  mainly  on  those  streams,  the  temperature, 
of  any  place  must  be  made  greatly  to  vary,  in  different 
ages  of  the  earth's  history. 


Diagram  showing  the  change  of  Behring's  Strait  necessary  to  warm 
Northern  Regions. 


CHAPTER   V. 


IEREGULAKITIES  OF  THE  EARTH. 


LESSON  I. 
HILLS,  MOUNTAINS,   VALLEYS,   AKD  CONTINENTS. 

r"PHE  surface  of  the  earth  abounds  in  irregular  eleva 
-*-  tions,  which  have  been  formed  in  various  ways. 
When  the  running  water  has 
cut  away  about  a  mass  of 
earth  or  rock,  we  term  it  a 
hill.  The  figure  shows  the 
form  of  a  hill,  the  dotted  lines 
showing  the  rock  that  has 
been  cut  away  in  its  forma- 
tion. As  nearly  every  region 
has  had  running  water  upon 
it,  hills  are  found  every- 
where. Mountains,  at  first 
sight,  look  like  greater  hills, 
but  we  find  that  they  are 
built  in  a  different  manner. 
They  are  made  by  a  folding 
of  the  rocks  of  which  they 
are  composed,  as  shown  in 
the  figure.  These  rocks  were 
originally  flat,  lying  like  those  Fif/.  49. 

in    the    hill,    but,     by    a    Way  Section  of  Mountain. 


Fig.  48. 
Section  of  Hill. 


108  IRREGULARITIES   OF   THE  EARTH. 

which  we  will  now  consider,  they  have  been  crumpled  up 
so  that  they  lie  like  a  mass  of  wrinkled  paper.  If  we 
look  closely  at  any  mountain,  we  see  that  a  great  part  of 
it  has  been  cut  away  by  rivers,  so  that  the  hill-making 
forces  are  as  evident  there  as  elsewhere.  We  may  prop- 
erly say  that  every  mountain  is  in  a  certain  sense  a  hill, 
while  hills  proper  are  net  mountains. 

The  cause  of  this  crumpling  of  the  rocks  in  a  moun- 
tain is  a  pressure  coming  horizontally  through  the  earth. 
We  may  represent  it  by  taking  a  number  of  sheets  of 
paper,  each  of  which  may  stand  for  a  layer  of  rock,  and 
pressing  them  from  the  siples,  so  that  they  may  be  forced 
to  wrinkle,  as  shown  in  the  figure.  This  is  the  way  in 
which  this  wrinkling  is  brought  about: 

The  earth  is  very  hot  in  the  inside,  as  we  know  from 
the  fact  that  volcanoes  throw  out  masses  of  rock  melted 
by  heat,  and  that  all  our  mines  grow  hotter  as  they  de- 
scend. Now,  the  space  outside  of  the  earth  is  extremely 
cold,  as  is  shown  by  the  fact  that  all  very  high  mountains, 
even  under  the  tropics,  have  snow  that  does  not  melt  in 
midsummer.  If,  in  the  hottest  summer  day,  we  should 
ascend  to  the  height  of  five  miles  above  the  earth,  we 
should  find  the  air  at  about  zero.  This  heat  of  the  earth's 
depths  is  constantly  leaking  out  into  the  spaces  of  the 
sky ;  enough  passes  off  each  day  to  melt  somewhere  about 
one  hundred  cubic  miles  of  ice.  Now,  as  the  earth  loses 
heat,  it  shrinks.  All  substances,  except  water,  shrink  in 
cooling.  A  familiar  example  of  this  is  seen  in  the  rails  of 
a  railway.  In  the  heat  of  summer,  they  swell  until  their 
ends  come  close  together ;  in  the  winter,  they  shrink  until 
they  are  some  distance  apart.  A  mass  of  melted  stuff, 
Buch  as  glass,  will  generally  become  one-tenth  smaller 
when  it  loses  enough  heat  to  freeze  or  become  solid 


HILLS,   MOUNTAINS,    VALLEYS,   AND   CONTINENTS.    109 

From  this  loss  of  heat,  the  earth  constantly  becomes 
smaller.  Take  any  point  in  our  solid  rocks :  it  is  certain 
that  one  thousand  years  ago  this  point  was  a  little  further 
from  the  earth's  centre  than  at  present,  because  the  shrink- 
ing of  the  earth  in  one  thousand  years  amounts  to  a  foot 
or  more  of  its  diameter.  In  this  shrinking,  it  is  the  deeper 
part  of  the  earth  that  grows  smaller.  The  outer  part, 
that  is  folded  into  our  mountains,  has  long  been  so  cooled 
that  it  had  no  great  amount  of  heat  to  lose,  and  so  of  late 
it  has  not  shrunk.  All  the  inner  region  has  been  steadily 
shrinking  since  the  world  began.  It  is  easy  to  see  that  thi& 
outer  part  must  wrinkle  on  the  outside.  To  compare  small 
things  to  great,  we  may  con- 
sider an  apple  as  representing 
the  earth,  and  its  skin  as 
answering  to  the  cold  outer 
shell.  When  the  apple  dries 
up,  the  outer  skin  wrinkles, 
because  it  loses  a  little  of 
the  water  that  escapes.  Con- 
ceive a  loss  of  heat  to  bring 
about  the  shrinkage  in  the  Fig.  so.  Wrinkling  of :  Earth  or  Apple, 
apple,  and  we  have  a  close  likeness  between  the  little  sphere 
of  the  fruit  and  the  world  that  gave  it  life. 

If  our  mountains  had  not  been  worn  down  by  the 
action  of  water,  they  would  appear  vastly  higher  than 
they  are.  The  very  highest  has  its  top  less  than  six  miles 
above  the  sea ;  but,  if  we  could  put  on  it  all  that  the  water 
has  worn  away,  it  would  probably  be  twice  as  high. 

Yet  it  must  not  be  supposed  that  these  mountains  were 
ever  much  higher  than  at  present ;  for,  in  fact,  the  moun- 
tains grow  slowly  upward,  while  the  streams  of  running 
water,  or  the  ice  streams  that  often  form  in  their  high-up 


110  ^REGULARITIES   OF   THE   EARTH. 

valleys,  cut  them  down.  So  slowly  do  our  mountains 
generally  lift  themselves,  that  a  stream  flowing  across 
them  is  sometimes  able  to  keep  its  bed  cut  open  as  the 
mountain  rises,  the  ridge  never  moving  upwards  so  sud- 
denly that  the  river  found  an  impassable  dam  in  its  way. 

The  simplest  mountains  are  like  the  Alleghenies,  where 
a  number  of  long,  low  ridges,  looking  something  like 
boats  turned  upside  down,  lie  side  by  side,  closely  crowded 
together.  In  more  complicated  mountains,  the  smaller 
folds  rest  upon  larger  folds,  as  shown  in  the  figure  below, 
the  whole  worn  down  in  a  curious  way  by  the  streams.  It 
is  in  such  mountains  as  the  Alps,  where  we  have  this  very 


Fiif.  51.   Section  through  Mt.  Blanc. 

complicated   structure,  that  we  find  the  finest  mountain 
scenery. 

If  mountains  cease  to  grow,  the  streams  gradually 
plane  them  down  until  the  surface  becomes  nearly  level 
again,  and  only  a  geologist  can  see  that  the  country  has 
its  rocks  arranged  in  a  mountainous  way.  There  are 
many  countries  where  such  worn-down  mountains  occur, 
and  they  are  not  infrequent  in  America, — the  eastern 
part  of  New  England,  including  all  of  Rhode  Island  and 
the  most  part  of  Massachusetts  and  Maine,  is  upon  such 
worn-down  mountains. 


HILLS,   MOUNTAINS,   VALLEYS,   AND   CONTINENTS.    Ill 

One  of  the  advantages  of  this  peculiar  structure  is,  that 
it  enables  us  to  get  at  many  stores  of  mineral  wealth, 
from  which  we  would  otherwise  have  been  debarred  by 
their  deep  burial.  We  see 
by  the  diagram  how  a  seam 
of  coal  or  a  bed  of  iron  ore 
may  be  brought  to  the  light, 
which  otherwise  would  have 
been  deeply  buried  in  the 
earth,  beyond  the  reach  of 
man. 

Mountain  ridges  are  rarely 
found  alone.  When  they  ^-52-  Coal  Beds  opened  by  Fold, 
occur  at  all,  they  are  generally  in  long  sets  of  ridges, 
which  have  each  the  same  general  direction  as  the  main 
chain.  A  familiar  instance  of  this  is  seen  in  the  ridges  of 
the  Allegheny  mountains  or  of  the  larger  Appalachian 
series  of  mountains,  of  which  the  Alleghenies  form  but  a 
part.  Rather  more  than  one-half  of  the  earth's  surface 
has  been  pushed  into  the  crumpled  form  of  mountain 
folds.  In  fact,  nearly  every  part  of  our  rocks  that  has 
been  made  for  a  long  while  shows  some  marks  of  crump- 
ling under  this  pressure  that  builds  mountains,  and  in 
time  even  the  most  level  rocks  will  probably  be  twisted 
by  this  force  pressing  against  their  sides. 

These  foldings  of  the  rocks  may  be  of  any  size,  from 
those  that  form  the  greater  mountains  down  through  those 
of  less  and  less  dimensions,  until  the  fold  is  only  an  inch 
or  so  in  width.  In  the  larger  folds,  the  thickness  of  the 
folded  rocks  is  great ;  while,  in  the  smaller  folds,  the  beds 
may  not  be  thicker  than  this  paper. 

Besides  the  steep,  sharp  foldings  in  the  mountains,  the 
earth's  crust  has  folded  in  broader  curves  to  form  the 


112  IRREGULARITIES   OF   THE   EARTH. 

continents  and  great  basins.  These  folds  are  immensely 
broad  and  of  very  gentle  curves.  Thus,  while  a  moun- 
tain may  be  nearly  as  high  as  it  is  broad,  the  continental 


Fig.  53.  Section  across  North  America. 


fold  is  from  one  hundred  to  one  thousand  times  as  wide  as 
it  is  high.  It  is  not  certain  just  how  these  continents  are 
formed,  but  they  probably  arise  from  the  folding  of  thicker 
parts  of  the  earth's  crust  than  are  crumpled  together  in 
the  formation  of  mountains,  —  a  folding  that  is  also  due 
to  the  gradual  escape  of  heat  from  the  earth's  interior. 

It  is  worth  our  while  to  notice  that,  although  the  heat 
that  comes  to  the  earth  from  the  sun  and  stars  serves,  by 
setting  in  motion  the  machinery  of  the  rains  and  waves,  to 
wear  down  the  mountains  and  the  continents,  the  heat  that 
goes  from  the  interior  to  the  stellar  spaces  causes  the 
mountains  and  continents  continually  to  rise  and  replace 
the  wear  effected  by  the  ever-falling  heat.  The  heat,  fall- 
ing on  to  the  earth,  tends  to  reduce  all  its  irregularities 
to  a  plane  ;  the  heat  that  flies  upward  from  its  depths  serves 
to  make  it  irregular,  —  to  build  mountain  and  continent  as 
fast  as  rain  and  wave  wear  them  down. 


CHAPTER   VI. 


ORIGIN  OF   VALLEYS  AND  LAKES. 


LESSON  I. 
RIVER    VALLEYS. 

A  LTHOUGH  the  continents  and  mountains  form  the 
-^-  greatest  irregularities  of  the  earth's  surface,  there 
are  other  and  commoner  features  in  the  land  that  we  can- 
not pass  by.  Nearly  every  part  of  the  earth's  surface, 
above  the  line  of  the  sea,  is  formed  into  valleys,  and  in 
many  of  these  valleys  there  are  deposits  of  fresh  or  salt 
water,  termed  lakes. 

These  valleys  are  of  all  scales  of  magnitude,  from  those 
that  may  be  bridged  with  the  foot,  to  those  that  include 
half  a  continent  within  their  bounds. 

To  understand  how  valleys  are  formed,  we  should 
observe  the  action  of  rain-water  on  some  area  of  smoothed 
land,  such  as  a  newly-ploughed  field  over  which  a  roller  has 
been  drawn,  bringing  its  surface  to  an  even  slope.  We  see 
that  the  water  at  once  carves  out  for  itself  a  system  of 
channels  which  connect  with  each  other,  so  that  a  picture 
of  these  streamlets  will  look  something  like  a  map  of  any 
large  river  system. 

Whenever  the  seas  give  up  the  lands  to  the  air,  they 
are  at  once  seized  upon  by  the  rain-water,  and  their  sur- 
face brought  into  such  a  system  of  valleys ;  the  only 
exceptions  being  when,  as  is  the  case  on  only  a  few  spots 


114  ORIGIN  OF   VALLEYS   AND   LAKES. 

upon  the  earth's  surface,  there  is  too  little  rain  to  make 
any  rivers  at  all. 

Each  of  these  river  valleys  has  certain  features  which 
are  common  to  all  others,  though  no  two  are  just  alike. 
Every  river  valley  has  three  principal  parts :  the  place 
where  the  river  is  actually  cutting  its  way,  which  is 
termed  the  channel;  the  alluvial  plain  on  either  side;  and 
the  far  wider  section  on  either  side,  which  is  termed  the 
water-shed  of  the  river. 

The  relative  proportion  and  relations  of  these  two  ele- 
ments of  the  valley  vary  very  much,  which  gives  the  most 
of  the  variety  to  our  river  basins. 


Fig.  54. 
Section  across  River  Valley. 

The  channel  of  the  river  is  principally  due  to  its 
mechanical  cutting  power  on  the  rocks  through  which  it 
goes.  On  either  side,  the  alluvial  plain  marks  the  place 
where  the  stream  has  recently  been  at  work,  but  from 
which  it  has  swung  away.  On  either  side,  but  further 
away  from  the  channel,  is  a  broad  slope  towards  the  stream, 
which  may  be  miles  in  width,  and  is  nearly  always  cut  up 
by  tributary  streams,  each  essentially  like  the  main  river: 
only  smaller. 

To  get  a  good  idea  of  a  river's  history,  we  should  go 
to  some  of  its  mountain  tributaries,  —  for  all  very  large 


RIVER    VALLEYS.  115 

rivers  head  in  mountains,  —  see  there  the  first  steps  of 
the  water ;  then  trace  this  stream  to  the  sea.  In  thiu 
mountain  stream  we  shall  find  the  water  rushing  rapidly 
down  a  steep  slope  cut  in  the  solid  rocks.  These  rocks 
themselves  are  the  waste  of  old  rivers,  which  was  long  ago 
carried  to  the  sea  from  old  lands,  built  on  the  sea-floor, 
and  uplifted  into  the  land  again,  where  we  find  the  river 
now  carving  them.  They  may  be  in  the  shape  of  sand- 
stones, shales,  and  limestones,  or  they  may  have  been 
altered  by  heat  into  the  .shape  of  granites  or  other  crys- 
tallized rocks.  We  shall  find  the  mountain-stream  bed  full 
of  great  rounded  or  angular  stones,  which  have  been  riven 
from  the  banks  by  the  roots  of  trees  or  the  frost,  or  released 
by  the  process  of  decay,  which  works  into  every  fissure  of 
the  rocks,  and  leaves  them  free  to  fail.  In  the  dry  season, 
the  clear  water  of  the  stream  tumbles  about  among  the 
stones,  making  a  great  deal  of  noise,  but  doing  little  work 
of  wearing  ;  but  in  the  times  of  flood  we  shall  find  it  full 
of  muddy  water,  and  we  may  see  the  large  stones  pounding 
along,  bruising  their  neighbors,  and  wearing  the  bed  over 
which  they  are  forced  to  move.  Now  and  then,  land- 
slides bring  a  great  amount  of  rubbish  into  the  bed,  so 
that  the  stream  is  dammed  for  a  time ;  but  its  waters 
soon  overcome  the  barrier,  and  bear  its  earth  and  stones 
on  in  the  flood.  These  times  of  flood  are  the  only  occa- 
sions when  the  stream  becomes  a  rock-grinding  mill ;  and 
its  power  is  due  to  the  swiftness  of  the  waters,  and  the 
ease  with  which  they  urge  the  stones  down  the  steep 
slope  of  the  bed.  In  this,  the  torrent  part  of  a  river,  the 
stream  generally  falls  fifty  feet,  or  more,  to  the  mile.  If 
its  slope  is  steeper,  it  often  clears  away  the  greater  part 
of  the  stones,  and  flows  over  the  lower  rock-bed. 

Soon  the  brook,  swollen  by  tributaries  from  either  side, 


116  ORIGIN   OF   VALLEYS    AND    LAKES. 

finds  its  way  out  of  the  gorge  in  which  it  was  born,  and 
enters  a  wider  valley,  where  it  falls  less  rapidly,  and  takes 
on  the  character  of  a  little  river.  The  first  change  we 
notice  is  that  the  river  no  longer  flows  in  a  narrow,  V-- 
shaped gorge,  with  110  flat  land  along  it,  but  it  now  has 
a  little  edge  of  stones,  sand,  and  earth  on  either  side  of 
its  waters.  Here  lie  the  bits  of  stone  which  its  dimin- 
ished current  no  longer  permits  it  to  carry ;  for  the  swift 
streams  above  send  down  larger  pebbles  than  the  river 
can  now  carry  away.  They  have  to  remain  until  they  are 
decayed  into  pieces  small  enough  for  the  stream  to  bear 
onward.  As  we  descend  further  towards  the  mouth,  we 
find  that  the  current,  except  for  occasional  falls  or  rapids, 
becomes  constantly  slower,  so  that  these  stones  lodge  on 
the  sides  of  the  stream,  making  wider  and  wider  terraces 
on  either  side  of  its  path.  This  accumulation  of  rubbish 
causes  the  stream  frequently  to  change  its  bed.  In  these 
ways  it  cuts  away  on  one  side  of  the  alluvial  deposit, 
and  fills  in  011  the  other.  Each  time  it  travels  over  the 
deposits  of  pebbles,  it  takes  out  the  part  that  is  decayed  to 
sufficient  fineness  to  be  borne  along;  the  larger  pieces 
soon  lodge  again  in  the  terrace-beds. 

When  the  stream  is  at  its  flood  height,  it  commonly 
overflows  much  of  this  alluvial  plain,  and  leaves  on  it 
a  coating  of  fine  mud,  which  is  generally  built  into  a 
very  fertile  soil.  This  soil  is  often  very  deep,  but  below 
it  we  find  the  layer  of  stones  which  the  stream  had  not 
force  enough  to  carry  with  it. 

Near  the  mouth  of  a .  great  river,  these  alluvial  lands 
rapidly  widen,  and  form  the  delta,  which  is,  in  reality, 
not  a  thing  by  itself,  but  is  the  broadened  ends  of  the 
alluvial  plains  that  border  the  stream,  from  the  time  it 
became  a  river ;  that  is,  when,  in  its  head-waters,  the  fall 


EIVER    VALLEYS.  117 

of  its  bed  became  too  slight  to  carry  all  the  rubbish  the 
mountain  torrents  sent  into  it. 

The  only  striking  variety  given  to  a  river  is  where 
some  harder  rocks  cross  its  bed,  making  a  fall.  Falls 
are  formed  in  several  ways.  One  way  is  when  a  trap 
dyke  crosses  a  stream,  forming  a  dam  of  rock  so  hard  that 
the  stream  has  difficulty  in  cutting  through  it.  Such 
falls  are  rare ;  they  hardly  occur  in  any  great  streams. 
Another  and  commoner  way  is  when  the  bedded  rocks  that 
cross  the  stream  slope  down  towards  its  head,  as  shown  in 
the  diagram,  Fig.  55.  In  this  case,  if  there  be  a  hard  bed 
also  with  soft  rocks  below  it,  a  fall  will  be  formed.  The 
water  plunges  over  the  hard 
bed,  and,  by  dashing  the 
stones  about,  wears  away  the 
soft  bed,  making  a  steep  and 
often  an  over-hanging  cliff. 

The  falls  of  Niagara,  as  rep- 
resented in  the  diagram,  are 
formed  in  this  way.  On  top 
is  a  hard  limestone,  known 

to    geologists   as    the    Niagara      Fil-'-  M-    Section  of  Niagara  Falls. 

limestone,  which  happens  to  cross  the  river  at  this  point  ; 
below  is  a  soft  slate,  which  the  whirling  waters  at  the 
foot  of  the  fall  easily  cut  away.  From  time  to  time,  this 
undercutting  causes  the  overhanging  hard  layer  to  fall  to 
the  base,  where  the  surging  waters  use  the  fragments  as 
tools  to  cut  away  still  more  of  the  soft  layer.  In  this 
work,  the  beating  spray,  which  lashes  against  the  rock, 
gives  much  help.  So  the  fall  is  slowly  working  up  stream, 
at  the  rate  of  a  few  feet  in  a  hundred  years.  All  falls 
of  this  nature  work  up  stream  in  the  same  fashion,  be- 
coming lower  as  the  hard  layer  sinks  downwards  towards 


118 


ORIGIN    OF    VALLEYS    AND    LAKES. 


the  stream-bed ;  as  will  be  easily  seen  by  inspecting  the 
diagram  of  Niagara  Falls. 

The  falls  of  the  Ohio,  at  Louisville,  afford  yet  another 
and  the  rarest  sort  of  fall.  There  the  river  flows  over  an 
old  coral  reef,  which  was  built  into  rocks  formed  long 
before  the  coal  measures.  This  coral  reef  is  much  harder 
than  the  other  rock  of  the  country,  so  that  the  river  is 
thrown  into  cascades  where  it  crosses  its  surface. 

This  is  a  brief  account  of  the  course  of  the  water  in 
the  stream  itself,  and  of  the  causes  that  give  its  course 
and  shape  its  bed.  The  causes  of  river-courses,  and  the 
many  details  of  its  shape,  are  not  easily  understood,  and 


Fiy.  56.    Change  of  River  Channels. 

depend  on  a  thousand  local  conditions.  The  constant 
swings  of  a  river  are  made  to  get  away  from  the  waste 
which  its  current  is  continually  trying  to  bear  along;  a 
work  which,  from  the  quantity  of  this  waste,  it  cannot 
well  do.  All  our  rivers  are  overburdened  by  their  sedi- 
ments. In  their  struggle  with  the  waste,  they  are  thrown 
into  strange  turns  and  windings,  called  ox-bows,  which 
are  found  only  in  sluggish  parts  of  streams.  These  ox-bows 
are  often  cut  across  by  the  current,  leaving  what  are  some- 
times called  moats,  from  their  likeness  to  the  ditches  dug 
about  old  castles,  and  other  tower  strongholds. 


RIVER    VALLEYS.  119 

The  bed  of  a  river,  though  it  seems  to  move  mainly  to  and 
fro  through  its  alluvial  plain,  is  generally  cutting  downward 
into  the  rock  that  underlies  it ;  the  result  is,  that  it  leaves 
more  or  less  of  these  alluvial  fields  high  upon  the  banks 
on  either  side  of  the  stream.  These  shreds  of  the  old 
alluvial  plains  show  the  successive  levels  of  the  stream, 
as  it  has  cut  downward  in  its  endless  wearing  of  the  rocks 
over  which  it  flows.  Sometimes  there  are  as  many  as 
half  a  dozen  of  these  old  levels  marked  in  the  terraces 
of  the  stream.  Very  good  examples  of  these  occur  along 
the  Connecticut  River,  and  most  of  the  other  New  Eng- 
land streams.  They  have  been  considered  as  proofs  that 


Fiy.  57.     Terraces  of  Kiver  Gravel. 

the  river  was  once  much  larger  than  it  now  is,  but  this 
is  not  the  case ;  for,  if  the  river  had  ever  been  able  to  fill 
its  valley  to  the  level  of  these  high  terraces,  it  would  have 
swept  them  away  altogether  on  account  of  the  swiftness 
of  its  stream.  The  diagram  shows  the  general  position 
of  terraces  in  a  river  valley,  and  the  old  levels  of  the 
river  when  they  were  formed.  We  must  imagine  that, 
at  each  level,  the  river  swung  to  and  fro  a  great  deal, 
always  cutting  slowly  downwards. 

On  each  side   of  the  river,  as  before  remarked,  there 
is  a  gentle  slope  upward  to  the  "divide,"  or  separation 


120 


OBIGIN   OF   VALLEYS   AXD   LAKES. 


line  between  any  river  valley  and  the  next  adjacent 
stream.  This  slope  is  caused  in  part  by  the  cutting  of 
the  small  tributary  streams,  and  in  part  by  the  dissolving 
of  the  rock  by  the  water  percolating  through  the  soil. 


Fiy.  58. 
Divide  between  two  Streams. 


In  some  few  cases  where  a  stream  has  its  head-waters 
in  a  country  where  the  rainfall  is  large,  and  then  flows 
through  a  region  where  there  is  scarcely  any  rainfall,  the 
sides  of  the  stream  in  the  desert  region  have  no  chance 


Fig.  59. 
Colorado  Canor 


to  be  cut  down,  so  the  river  carves  out  a  very  deep  track, 
through  which  it  flows.  The  best  example  of  this  in  the 
world  is  the  great  Colorado  Canon,  where  the  river,  plen- 
tifully fed  at  its  head-waters  in  the  Rocky  Mountains, 
pours  for  a  long  distance  through  a  nearly  rainless  coun- 


RIVER    VALLEYS.  12j 

try,  where  it  has  carved  out  a  very  deep  bed  with  walls    • 
thousands  of  feet  high  on  either  side. 

In  a  few  cases  we  have  valleys,  such  as  the  famous 
Yosemite,  where  the  trough  through  which  the  river  flows 
was  probably  made  by  the  fracture  of  the  rocks  by  faults 
with  the  down-sinking  of  the  region  in  which  the  valley  lies. 

Sometimes,  as  in  the  case  of  the  Connecticut,  the  Merri- 
mac,  and  other  rivers  of  New  England,  the  river  valley  is 
first  carved  out  by  a  river,  and  then,  becoming  the  path- 
way of  a  glacier,  is  widened  by  the  ice  stream.  In  this 
way,  many  small  mountain  valleys  which  are  cut  into  V- 
shaped  trenches  by  rivers, 
have  been  changed  into  U- 
shaped  valleys  by  the  wider 
streams  of  ice  that  filled  them 
in  glacial  times.  This  is  be- 
cause the  swift-running  brook 
cuts,  at  any  one  time,  only 
the  narrow  space,  perhaps  ten 
feet  wide,  of  its  bed.  The 
slow  glacier  moves,  say,  three  fig.GO.  River  Gorge  widened  by  ice. 

feet  a  day,  while  the  living  water  floy/s,  say,  sixty  miles 
a  day ;  so  the  glacial  stream  is  necessarily  a  very  wide 
and  deep  one,  and  grinds  a  broad  channel. 

We  may  close  our  glance  at  river  valleys  by  stating 
that  they  represent  the  great  erosion  work  of  the  world. 
They  are  the  result  of  a  force  that  comes  to  the  earth 
through  sunshine,  and  acts  through  running  water,  work- 
ing to  bear  away  the  sediment  from  the  land  into  the 
sea,  where  it  may  be  made  to  nourish  life,  and  to  form 
new  strata  in  the  sea-floor,  —  strata  which  are,  it  may  be, 
destined  to  rise  again  into  lands,  to  be  again  subject  to 
the  wear  of  the  streams  in  ages  to  come. 


122  ORIGIN   OF  VALLEYS   AND   LAKES. 

Besides  the  valleys  carved  out  by  rivers,  and  the  forces 
that  produce  lakes,  there  are  some  great  valleys  that 
have  been  shaped  by  the  action  of  the  ocean  tides,  while 
the  lands  were  under  water.  Although  these  sea-carved 
valleys  are  rare,  it  is  worth  our  while  to  study  them,  as 
they  give  us  an  idea  of  the  way  in  which  wearing  goes  on 
upon  the  ocean  shore  and  on  the  bottom  of  the  sea  near 
the  land. 

The  winds  and  waves  which  the  sea  sends  against  the 
shore  have  no  power  of  cutting  valleys.  They  batter 
the  shore  most  effectively  on  the  headlands.  Their  waves 
weaken  as  they  enter  a  bay.  Thus,  in  time,  they  tend  to 
bring  the  coast  to  a  straight  line,  by  wearing  off  the  head- 
lands, and  filling  the  waste  into  the  inlets  between  the 
promontories.  The  tides,  however,  work  in  the  reverse 
way.  On  the  shores  of  the  ocean,  twice  each  day,  there 
is  from  the  deep  a  rush  of  water  that  passes  up  every 
indentation,  stirring  up  the  mud,  and  mixing  it  with 
the  water.  As  these  tides  go  out,  they  drag  back(  this 
dissolved  sediment,  and  draw  pebbles  along  the  bottom 
out  into  the  open  sea.  Now,  these  tide-waves,  unlike  the 
wind  waves,  rise  much  higher  in  the  heads  of  bays  and 
gulfs  than  they  do  on  the  shore;  and,  as  the  force  with 
which  they  scour  away  the  bottoms  of  the  bays  depends 
on  the  height  to  which  the  water  rises  with  each  tide,  the 
effect  of  tidal  action  is  often  much  greater  in  the  upper 
part  of  bays  than  at  their  mouths.  Thus,  the  Bay  of  Fun- 
day,  between  Nova  Scotia  and  New  Brunswick,  has  a 
tide  of  about  twenty  feet  at  the  mouth,  while  the  water 
rises  as  much  as  sixty  feet  in  the  interior  or  innermost 
part  of  the  bay.  The  result  is  that  the  tides  cut  away 
the  rocks  at  the  head  of  the  bay  with  far  more  force  than 
at  the  mouth. 


RIVER    VALLEYS.  123 

In  this  way  it  comes  about,  that  wherever  there  are 
strong  tides,  they  tend  to  cut  out  and  deepen  the  bays 
along  the  shore,  by  the  ceaseless  rushing  of  their  waters. 
Shores  with  strong  tides  are  in  this  way  almost  always 
much  cut  up  into  inlets  that  afford  good  harbors. 

Some  of  the  finest  instances  of  tide-cutting  are  found 
along  the  British  shores,  where  the  tides  are  generally 
strong.  The  channel  which  separates  Great  Britain  from 
France  and  Holland  has  doubtless  been  cut  through  by 
the  tides.  The  mouth  of  the  Thames  and  of  the  Severn 
have  been  greatly  scoured  out  by  the  same  action.  The 
Chesapeake  and  Delaware  Bays,  on  our  own  coast,  are 
probably  due  to  this  cause.  Wherever  these  old  tidal 
bays  are  elevated  above  the  sea-level,  they  appear  as 
very  broad  valleys  through  which  a  stream  flows.  Gradu- 
ally they  are  changed  in  shape  until  they  look  much  like 
river  valleys.  For  a  long  time  the  steep  cliffs  on  either  side 
show  the  action  of  the  sea ;  but  gradually  these  are  worn 
down,  and  we  can  no  longer  tell  that  the  valley  was  formed 
by  the  tides. 

As  the  sea  is  constantly  rising  and  falling  along  the 
lands,  it  is  likely  that  the  lower  parts  of  all  our  large 
streams  have  had  their  shape  in  part  determined  by  the 
tidal  forces.  We  can  see  the  marks  of  this  work  near  the 
mouths  of  the  Connecticut,  Hudson,  Delaware,  and  all 
the  more  northern  rivers  on  the  eastern  shore  of  this  con- 
tinent, as  well  as  the  northern  rivers  of  Europe. 

This  tidal  force  comes  upon  the  earth  from  the  attrac- 
tion of  the  sun  and  moon  on  all  the  matter  composing  the 
earth.  The  land  is  too  rigid  to  give  way  to  the  impulses, 
but  the  fluid  waters  swing  in  the  broad  waves  of  the 
tides. 

These  tidal  waves  produce  only  a  few  geological  effects 


124 


ORIGIN    OF    VALLEYS    AND    LAKES. 


of  importance.  Besides  cutting  out  the  bays  along  the 
shore,  they,  by  their  currents,  carry  a  good  deal  of  sedi- 
ment from  the  shore,  and  lodge  it  on  the  bottom  some 
distance  out  to  sea,  forming  a  broad  under-water  shelf 
along  the  coast. 


Fiy.  61 .   Channels  carved  out  by  Tides. 

The  currents  that  the  tides  produce  in  every  part  of 
the  oceans  serve  also  to  feed  many  forms  of  life  that  are 
fixed  to  the  bottom  of  the  sea,  and,  therefore,  unable  to 
seek  their  food.  As  the  waters  drift  by  them,  on  the 
tide,  they  can  grasp  it  with  their  tentacles,  and  carry  it  to 
their  mouths. 


LAKES.  125 

LESSON   II. 

LAKES. 

AMOXG  the  most  beautiful  features  of  the  lands  are  the 
lakes.  It  is  rather  because  of  their  beauty,  than  because 
they  are  very  important  features  in  the  mechanism  of  the 
earth,  that  we  shall  give  a  brief  account  of  them.  They 
are  very  interesting  to  the  student  of  nature,  for  the  reason 
that  they  show  many  curious  wpys  in  which  the  forces  of 
earth  and  air  have  worked  to  produce  the  form  of  the  lands. 

First,  let  us  notice  that  lakes  are  very  irregularly  scat- 
tered over  the  earth's  surface :  there  are  certain  regions, 
such  as  New  England,  where  the  land  is  sown  with  them; 
indeed,  the  whole  of  North  America  down  to  the  latitude 
of  about  40°  abounds  with  them,  while  south  of  that  region 
they  are  very  rare,  indeed ;  so  that,  while  Massachusetts  has 
several  thousand,  counting  those  above  an  acre  in  area, 
there  are  many  Southern  States  that  have  hardly  a  single 
water  basin  that  can  fairly  be  called  a  lake. 

Lakes  are  so  different  in  their  form  that  they  have  only 
one  common  character :  they  are  basins  containing  water 
separated  from  the  main  seas,  so  that  if  there  is  any  water 
connection  at  all  with  the  ocean,  it  is  by  means  of  a  river. 
We  may  divide  these  land  water-basins  into  two  great 
classes  of  salt  lakes  and  fresh-water  lakes.  Nearly  all 
lakes  are  fresh,  but  here  and  there  we  find  basins  contain- 
ing very  salt  water.  These  salt  lakes  are  always  without 
any  outlet  into  the  sea ;  the  reason  they  do  not  fill  up  the 
basins  in  which  they  lie,  and  overflow  into  the  ocean,  is 
that  the  streams  that  feed  them  cannot  make  head  against 
the  evaporation  which  the  sun  brings  about,  —  their  water 


126  ORIGIN   OF   VALLEYS   AND   LAKES. 

steams  away  into  the  clouds  as  fast  as  the  rivers  bring  it  in. 
If  the  rainfall  of  the  region  about  our  great  American  lakes 
should  gradually  diminish  so  that  it  would  amount  to  only 
one-third  of  what  it  now  is,  the  Niagara  River  would  shrink 
gradually,  and  in  the  end  no  longer  flow  over  the  falls. 
Then  the  water  in  the  basins  of  Lakes  Erie,  Huron,  and 
Michigan  would  still  further  shrink  until  the  evaporation 
from  the  remaining  surface  just  equalled  the  amount  the 
streams  sent  into  their  basins.  In  this  shape  their  waters 
would  slowly  cease  to  be  fresh,  and  in  the  course  of  ages 
they  would  become  salter  than  the  sea.  This  is  brought 
about  in  the  following  way:  Every  stream  flowing  into 
the  basin  carries  a  little  of  the  various  salts  that  make 
the  sea-water  saline ;  when  this  water  dries  away  in  the 
basin,  the  salt  is  left  behind,  for  such  substances  cannot 
go  away  with  the  watery  vapor.  The  result  is,  the  water 
finally  comes  to  have  more  salt  than  it  can  hold,  and  this 
extra  charge  is  laid  down  in  crystals  on  the  lake  floor. 
This  is  the  way  in  which  the  great  beds  of  rock-salt  have 
been  formed,  such  as  are  found  in  many  ancient  rocks. 
Wherever  these  thick  beds  of  rock-salt  have  been  formed, 
we  may  know  that  the  waters  in  the  olden  time  have 
been  completely  evaporated  by  the  sun;  and  this  can  only 
happen  where  basins  of  water  are  cut  off  from  free  connec- 
tion with  the  sea-water  through  rivers  that  discharge  their 
waters  into  the  sea,  such  as  those  which  drain  all  our  fresh- 
water lakes. 

Turning  now  to  consider  the  ways  in  which  the  basins 
that  contain  lakes  are  formed,  we  perceive  that  they  are 
made  by  different  causes  in  different  parts  of  the  earth. 
In  the  regions  north  of  40°  of  north  latitude,  nearly  all  the 
lakes  have  had  their  basins  cut  out  by  the  moving  ice  of  the 
glacial  time.  The  most  of  the  lakes  of  New  England  have 


LAKES. 


127 


been  formed  in  this  way,  or  are  due  to  the  dams  of  gravel 
and  sand  which  the  glacial  streams  have  left  across  the  val- 
leys. The  same  is  true  of  the  lakes  in  Europe,  even  as  far 
south  as  those  of  Italy.  It  is  not  easy  to  conceive  just  how 
the  ice  acted  to  dig  out  basins 
in  the  rock;  but,  if  we  exam- 
ine the  ground  beneath  a  gla- 
cier, as  we  may  do  in  many 
places,  we  find  that  the  ice 
eats  the  soft  rock  away,  leav- 
ing the  harder  ;  when  the 
glacier  disappears,  the  surface 
of  rock  is  left  with  hollows 

upon     it,    Which    form     little  ^-62-    Rock  and  Glacier. 

lakes,  until  they  become  filled  up  or  have  their  boundary 
ridges  cut  through  by  streams. 

When  the  great  glacier  of  North  America  passed  away, 
it  left  the  surface  with  thousands  of  these  rock  basins 
upon  it. 

The  greater  part  of  them  have  become  filled  up,  but 


j.  G3. 
Moraine  and  Lakes. 


many  still  remain  open.  Then  the  rubbish  of  the  glacial 
period  made  dams  across  many  hollows,  or  its  surface  was 
irregular,  enclosing  valleys  in  which  lakes  gathered,  as  is 
fihown  in  the  figures. 


128  ORIGIN   OF   VALLEYS   AND   LAKES'. 

The  very  irregular  surface  given  to  the  land  by  the  ice* 
action  of  a  glacial  period  may  be  seen  by  looking;  at  any 
of  our  northern  shores  from  Boston  to  Greenland  or  in 
Scandinavia.  We  see  that  these  shores  are  fringed  with 
islands,  and  cut  into  innummerable  bays.  This  is  be- 
cause the  surface  of  the  land  has  been  made  so  irregu- 
lar by  the  grinding  of  the  ^ce.  If  the  sea  had  made  its 
shore  in  any  part  of  the  continent  of  North  America  north 
of  the  great  lakes,  it  would  have  much  the  same  irregular- 
ity of  coast.  On  looking  at  a  good  atlas  of  the  world,  we 
notice  that  those  northern  shores  which  lie  in  regions 
ground  over  by  the  ice  during  the  glacial  period  generally 
have  these  irregular  shore-lines,  while  those  of  regions  near 
the  equator  generally  have  straight  coasts.  Another  way 
in  which  lakes  are  formed  is  this:  A  great  part  of  our 
little-changed,  stratified  rocks  are  easily  dissolved  by  water. 
Limestone  beds,  or  beds  containing  rock-salt,  etc.,  melt 
down  and  are  dissolved  by  the  long-continued  action  of 
water.  We  see  how  this  comes  about  if  we  study  the 
shores  of  such  a  basin  as  Lake  Ontario :  the  waves  beating 
against  the  shores  break  down  and  grind  up  the  soft  rocks ; 
the  lime  and  other  easily  dissolved  substances  mingle  with 
the  water  and  pass  away  to  the  sea ;  the  quartz  or  sand- 
grains  partly  dissolve  and  in  part  are  washed  away  into 
the  deeper  water  of  the  lake.  In  this  way,  all  our  great 
lakes  are  increasing  their  surfaces  and  diminishing  their 
depths. 

Although  this  is  rather  more  a  means  of  enlarging  than  of 
creating  lakes,  it  is  likely  that  some  of  the  great  lakes  of 
the  world  have  originated  by  this  dissolving  action  of  waters 
acting  on  beds  of  rock-salt  or  other  easily  dissolved  mate- 
rials. 

There  is  a  third  way  in  which  lakes  may  be  formed.  When 


LAKES.  129 

the  lands  rise  above  the  sea,  they  often  have  deep  pockets 
or  basins  in  them,  which,  when  they  are  lifted  above  the  sea- 
level,  become  lakes.  If  the  rainfall  of  the  country  is  large, 
these  basins  will  have  more  water  poured  into  them  than 
can  be  evaporated  by  the  sun ;  so  they  will  flow  over  at  the 
lowest  part  of  their  edge,  and,  in  time,  their  salt  water  will 
be  washed  out  of  them,  so  that  they  will  be  fresh-water 
lakes.  If,  on  the  other  hand,  the  rainfall  is  too  small  to 
fill  the  basin,  then  it  shrinks  to  a  lake  without  an  outlet, 
such  as  the  famous  Dead  Sea  of  Syria,  or  the  Salt  Lake  of 
Utah. 

In  some  cases  the  lake  is  formed  by  the  rising  of  a  moun- 
tain across  the  path  of  the  stream  ;  generally  the  mountain 
grows  so  slowly  that  the  stream  keeps  its  way  open,  but  in 
some  cases  the  mountain  lifts  too  fast  for  this  down-cutting 
of  the  river-bed  to  keep  pace  with  the  uplifting  of  the  dam: 
then  a  lake  is  formed,  which,  in  time,  is  drained  by  the 
deepening  of  the  stream  bed. 

These  seas  of  the  land,  however  formed,  are  but  tempo- 
rary things ;  all  over  the  lands  we  find  the  floors  of  drained 
lakes ;  they  abound  in  the  desert  regions  of  the  Rocky  Moun- 
tains, in  Switzerland,  and  elsewhere.  We  may  look  forward 
to  the  time  when  all  the  lakes  that  now  exist  will  either  be 
filled  up  by  the  rivers  that  flow  into  them,  or  drained  by 
the  cutting  down  of  the  beds  of  the  streams  that  drain  away 
their  waters  to  the  sea.  But  new  glacial  periods  will  doubt- 
less create  new  basins,  and  others  will  be  made  by  the  dis- 
solving of  the  rocks,  or  by  the  irregular  rising  of  mountains 
or  the  lands  ;  so  that,  as  long  as  the  world  endures,  these 
beautiful  features  of  our  landscapes  will  doubtless  exist. 


CHAPTER 


MOVEMENTS  OF  THE  EARTH'S  SURFACE. 


LESSON  I. 
EARTHQUAKES. 

TpORTUNATELY  for  the  life  the  earth  bears  upon  it,  its 
surface  is  generally  so  steady  that  it  merits  the  name 
of  terra  firma,  the  firm-set  earth,  the  ancients  gave  to  it ;  yet 
at  times  this  earth's  surface  is  rudely  shaken  by  those  jars 
and  tremblings  we  call  earthquakes.  It  is  doubtful  if  the 
reader  has  ever  felt  such  a  quake,  because  in  the  greater 
part  of  North  America  as  well  as  Northern  Europe  they 
are  very  rare,  and  usually  so  slight  as  to  escape  notice ;  a 
little  rattling  of  the  window  panes,  or  a  slight  swaying  of 
things  hung  by  cords  from  the  ceiling,  being  all  that  com- 
monly tells  us  that  accidents  may  happen  within  the  earth 
that  disturb  its  usual  quiet.  But  in  other  lands  these 
shocks  are  much  stronger,  and  produce  the  most  wide- 
spread destruction  of  life  and  property. 

The  best  way  to  get  an  idea  of  the  power  of  such  shocks 
is  to  take  the  history  of  some  great  earthquake,  and  see 
how  it  affected  the  country  it  ravaged.  For  this  purpose 
we  will  take  first  the  earthquake  of  1755,  which  in  good 
part  destroyed  the  city  of  Lisbon,  in  Portugal ;  not  because 
this  is  by  any  means  the  most  violent  or  the  most  destruc- 
tive to  life  of  the  many  thousand  great  shocks  that  are 


EARTHQUAKES.  131 

recorded,  but  because  it  shows  the  different  sorts  of  acci- 
dents that  may  happen  in  such  convulsions. 

On  the  first  of  November,  1755,  without  any  previous 
warning  from  the  lighter  shocks  that  often  foretell  the  com- 
ing of  a  great  earthquake,  a  noise  as  of  loud  thunder  was 
heard  within  the  earth,  beneath  Lisbon,  and  with  it  came  a 
convulsion,  which  in  a  few  minutes  laid  the  larger  part  of 
the  city  in  ruins.  Out  of  a  population  of  about  two  hun- 
dred thousand  persons,  over  sixty  thousand  perished.  Then, 
as  often  in  great  shocks,  a  portion  of  the  city  built  on  the 
hard  rocks  escaped  the  worst  ravages  of  the  earthquake, 
while  the  other  portions,  built  on  clay,  were  reduced  to 
heaps  of  rubbish.  Thousands  of  the  people  who  had 
escaped  from  the  falling  buildings  took  refuge  on  a  great 
marble  quay,  or  landing  place,  on  the  banks  of  the  river 
Tagus,  where  they  were  safe  from  the  falling  walls.  Sud- 
denly this  immense  structure  went  down  below  the  waters, 
carrying  the  crowd  of  people  with  it.  None  of  the  bodies 
ever  rose  to  the  surface ;  and,  when  the  place  was  sounded, 
very  deep  water  was  found  to  occupy  the  site  where  the 
quay  had  stood.  To  complete  the  work  of  destruction, 
there  came  another  of  the  calamities  that  often  attend 
earthquakes  on  the  ocean's  shore.  The  sea  slowly  retired 
for  a  long  distance,  so  that,  in  an  hour,  parts  of  its  bottom 
never  uncovered  before  were  bared.  Then  with  a  roar  it 
came  back,  in  a  wave  fifty  feet  in  height,  that  swept  over 
the  ruins,  giving  a  speedy  death  to  many  of  those  who  had 
been  imprisoned  in  the  falling  houses.  The  ships  in  the 
harbor,  which  had  been  saved  from  the  evils  of  the  earth- 
quake itself,  were  dashed  to  pieces  in  this  rush  of  waters. 

Thus,  in  this  earthquake,  we  have  the  three  forms  of  dan- 
ger which  these  calamities  may  bring  to  man :  the  shud- 
dering movement  of  the  ground,  the  engulfing  of  parts  of 


132  MOVEMENTS   OP    THE   EATCTH'S   SURFACE. 

the  surface  in  fissures  or  rents  in  the  earth,  and  the  form- 
ing of  vast  waves  in  the  sea  which  roll  in  great  floods  into 
the  streams. 

This  shock,  though  it  did  the  most  damage  at  Lisbon, 
and  hence  has  received  its  name  from  that  city,  shook  a 
portion  of  the  earth's  surface  larger  than  four  continents 
such  as  Europe.  In  Morocco,  a  town  with  over  eight  thou- 
sand people,  is  said  to  have  sunk  into  the  earth  as  sud- 
denly as  the  quay  at  Lisbon.  Even  in  Scotland  the  waters 
of  the  lakes  swayed  to  and  fro  as  the  earth  swung  beneath 
them.  The  hot  springs  at  Toeplitz,  in  Bohemia,  ceased 
for  awhile  to  flow,  and  then  burst  out  again  in  torrents  of 
discolored  water,  showing  that  the  deeper  part  of  the  earth 
there  had  been  strongly  shaken.  Far  out  at  sea  the  ships 
felt  the  shock  so  strongly  that  their  seams  were  opened,  and 
the  men  were  thrown  down  upon  the  decks.  The  disturb- 
ance of  the  ocean  reached  farther  than  the  shock  itself. 
The  sea  rolled  in  great  waves  on  to  the  shores  of  Madeira, 
and  even  in  the  West  Indies  it  rose  twenty  feet  above 
its  usual  level.  There  can  be  no  doubt  that  all  the  waters 
of  the  Atlantic  north  of  the  equator  were  swayed  by  the 
shock.  « 

It  is  likely  that  in  this  earthquake  more  than  one  hun- 
dred thousand  people  perished  outright,  and  that  thousands 
died  from  the  famines  and  pestilence  that  followed  from 
it;  so  that  in  this  convulsion  more  human  beings  perished 
than  in  any  battle. 

We  will  now  turn  to  another  earthquake  which  happened 
in  the  Island  of  Jamaica  in  1692,  which  shows  us  certain 
other  effects  of  these  shocks  which  are  not  so  evident  in 
the  Lisbon  earthquake.  This  beautiful  island  was  the  seat 
of  a  prosperous  colony  which  had  a  wealth  and  promise  ex- 
ceeding that  of  any  English  settlement  in  the  New  World. 


EARTHQUAKES.  133 

To  this  prosperity  the  earthquake  of  1692  struck  a  fatal 
blow.  In  this  series  of  shocks  the  ground  was  swept  to 
and  fro  in  a  succession  of  waves.  On  the  ridges  of  the 
earth-waves  cracks  opened,  and,  as  the  wave  rolled  on,  these 
fissures  closed  again.  People  were  engulfed  in  these 
chasms :  many  disappeared  entirely ;  others  were  thrown 
out  again  ;  yet  others  were  left  partly  buried,  but  squeezed 
to  death  in  the  jaws  of  the  fissures.  The  buildings  over 
the  water  sunk  down  in  a  standing  position  into  the  sea, 
and  were  long  visible,  with  their  tops  many  feet  below 
the  surface.  More  than  a  square  mile  of  land  around  the 
harbor  of  Port  Royal  was  thus  carried  below  the  sea.  The 
in-rush  of  the  sea  carried  a  frigate  over  the  tops  of  build- 
ings, and  left  it  on  the  roofs  far  from  the  shore. 

This  ruin  along  the  shore  was  equalled  in  the  interior 
of  the  island ;  though,  owing  to  the  fact  that  there  were  no 
large  towns,  there  the  loss  of  life  was  not  so  great.  The 
whole  surface  of  the  earth  was  so  moved  that  the  soil  on 
the  hillsides  slid  down  into  the  valleys  ;  the  rivers  ceased 
for  a  while  to  flow,  they  were  so  blocked  by  the  landslides. 
When  they  broke  through  these  masses  of  earth,  they  ran 
for  days  a  tide  of  mud  intermingled  with  timber  from  the 
land  that  had  slid  down  into  the  streams.  The  lofty  Blue 
Mountains,  which  the  hour  before  were  covered  with  ver- 
dure to  their  summits,  were  terribly  shaken  and  rent  by 
the  convulsion.  After  the  shock  they  appeared  half  bare 
from  the  landslides  that  had  carried  the  soil  into  the  valleys. 

The  United  States,  as  before  remarked,  is  mostly  free 
from  earthquakes.  There  are  only  four  regions  in  it  that 
have  ever  been  visited  by  shocks  of  much  violence.  One  of 
these  is  in  New  England  ;  another,  in  the  Mississippi  Valley, 
just  below  the  mouth  of  the  Ohio ;  a  third,  on  the  coast  of 
California  j  the  fourth,  in  the  eastern  part  of  South  Carolina. 


134  MOVEMENTS   OF    THE  EARTH'S   SURFACE. 

In  New  England,  there  have  been  three  pretty  strong 
earthquakes :  the  first  in  1685  ;  the  second  in  1727  ;  the 
third  in  1755.  Of  these,  the  last  two  were  very  violent. 
That  of  1727  lasted  for  several  years,  and  principally 
affected  the  region  near  Newburyport,  Mass.  It  was  a 
very  curious  disturbance ;  for,  while  the  shocks  —  of  which 
some  hundred  were  felt,  in  the  course  of  four  years  — were 
at  first  violent,  they  soon  became  slight.  The  strange 
feature  was  that,  with  each,  there  came  from  the  earth  a 
wonderful  thundering,  or  bellowing  noise,  loud  enough  to 
startle  people  from  sleep,  even  when  they  had  been  long 
used  to  it.  Many  believed  that  it  was  the  Evil  One  him- 
self, raving  in  his  empire  beneath  the  earth,  and  threaten- 
ing to  burst  it  asunder  in  his  rage.  We  shall  consider 
the  cause  of  this  noise  at  a  later  point  in  this  chapter. 

In  November,  1755,  occurred  the  greatest  earthquake 
that  ever  was  felt  in  New  England,  since  the  white  men 
came  to  the  country.  This  came  as  a  single  strong  shock, 
which  was  most  violent  at  and  near  Boston,  where  it  threw 
down  a  great  many  chimneys,  and  for  a  minute  or  so  was 
so  strong  that  people  could  not  keep  their  feet.  New 
England  had  then  mostly  wooden  buildings,  so  that  the 
destruction  of  property  was  small ;  but  such  a  shock  at 
this  day  would  be  very  dangerous  to  life,  and  would  cause 
a  vast  destruction  of  property.  In  that  day,  chimneys 
were  about  the  only  structures  likely  to  be  damaged  by  a 
moderately  strong  shock. 

The  Mississippi  Valley  has  had  but  one  great  earth- 
quake, a  succession  of  shocks,  which  began  in  November, 
1811,  and  lasted  until  1813.  The  first  of  these  quakes 
was  so  strong  that  it  probably  made  more  than  half  the 
continent  tremble  for  some  minutes.  The  shock  was  felt 
jn  Florida,  New  York,  Michigan,  and  the  West  Indies, 


EARTHQUAKES.  135 

Then  came,  from  day  to  day,  successive  shocks,  which 
constantly  shook  a  less  wide  extent  of  country,  until  there 
were  only  a  few  square  miles  of  land  that  trembled  at  the 
end  of  this  time  of  trouble.  The  worst  effects  of  the  move- 
ment were  felt  in  the  region  for  one  hundred  miles  south 
of  the  place  where  the  Ohio  River  enters  the  Mississippi. 
In  the  first  shock,  large  parts  of  this  region  sank  down 
to  the  depth  of  several  feet  below  the  former  level.  Into 
these  sunken  lands,  which  occupied  many  hundreds  of 
thousands  of  acres,  the  Mississippi  poured  its  waters  in 
such  a  flood,  that  for  some  hours  it  ceased  to  flow  towards 
the  gulf,  but  ran  back  towards  its  source.  The  ground 
opened  in  many  places,  spouting  up  jets  of  sand  and  water 
above  the  level  of  the  forest.  As  the  shocks  went  through 
the  forests,  the  trees  bent  over  and  locked  their  tops  into 
those  of  others,  or  beat  their  branches  to  pieces  in  mutual 
blows.  The  low,  strong  log  cabins  were  shaken  to  pieces ; 
and,  to  protect  themselves  from  the  constantly  opening 
and  closing  fissures,  the  people  cut  down  trees,  so  that 
they  fell  across  the  path  of  the  rents,  and  on  these  bridges 
they  built  shelters,  in  which  they  lived  for  months  before 
the  ground  became  steadfast  enough  to  be  trusted  again. 

So  great  was  the  ruin  of  the  land,  that  the  government 
was  compelled  to  help  the  people  to  find  new  homes  in 
districts  where  the  earthquake  had  not  done  such  damage- 
To  this  day  there  remain  many  marks  of  this  earthquake, 
though  near  three-quarters  of  a  century  have  passed  away. 
Reel  Foot  Lake  and  Obion  Lake,  large  sheets  of  water, 
were  formed  at  that  time.  Many  of  the  trees  which  were 
standing  on  the  submerged  land  still  lift  their  blasted 
trunks  above  the  water,  or  are  visible  below  its  surface. 

The  earthquakes  of  California  have  been  numerous  and 
violent.  The  only  one  that  led  to  any  destruction  of  life 


136  MOVEMENTS   OF    THE   EARTH'S   SURFACE. 

occurred  at  Santa  Barbara,  in.  1811,  or  at  about  the  same 
time  as  the  Mississippi  Valley  earthquake.  There  have 
been  many  dreadful  shocks  in  Central  America,  but,  as  a 
whole,  the  continent  of  North  America  has  fared  better 
than  any  other  of  the  great  lands  except,  perhaps,  Aus- 
tralia. The  worst  regions  for  earthquakes  are  found  in 
the  west  and  north  border  of  South  America,  southern 
Italy,  Asia  Minor,  and  parts  of  Central  Asia,  parts  of 
the  East  Indies,  Japan,  and  in  New  Zealand ;  while  in 
northern  Europe,  Australia,  South  Africa,  and  Brazil,  they 
rarely  happen.  But  every  part  of  the  earth  is  subject  to 
slight  shocks. 

It  was  once  supposed  that  there  was  some  relation 
between  earthquakes  and  volcanoes.  This  idea  came  from 
the  fact  that  every  volcano,  while  in  activity,  trembles 
with  repeated  shocks ;  sometimes  it  shudders  for  days  and 
months.  But  there  are  many  regions,  as  New  England, 
where  there  are  no  volcanoes  within  a  thousand  miles,  yet 
strong  earthquakes  here  occurred. 

In  trying  to  understand  the  cause  of  earthquakes,  we 
should  first  notice  the  theories  that  throw  light  on  their 
nature.  Experiment  shows  us  that  we  can  make  small 
earthquakes  by  exploding  gunpowder  underground,  or  in 
any  way  jarring  the  earth,  which  are  just  like  the  great 
shocks  in  everything  but  their  size.  Careful  study  has 
shown  us  that  all  earthquakes  are  of  the  same  nature  as 
the  jar  we  can  give  a  table  when  we  strike  it  a  blow  with 
a  hammer  or  with  the  clenched  hand.  If  we  throw  a 
stone  into  a  pool  of  water,  we  see  that  a  little  wave  rolls 
away  in  circular,  ring-like  wrinkles.  This  is  something 
like  an  earthquake  wave,  only  it  moves  very  slowly,  and 
an  earthquake  wave  very  rapidly.  If  we  strike  the  head 
of  a  drum,  a  succession  of  waves  flow  through  it.  This  is 


EARTHQUAKES.  137 

more  like  an  earthquake  wave.  If  we  strike  the  end  of  a 
long  timber  with  a  hammer,  a  person  holding  his  hand  on 
the  other  end  feels  a  jarring  motion  come  to  him  from 
the  timber.  This  is  exactly  like  an  earthquake  shock. 
In  the  pool,  the  drum,  and  the  stick  of  timber,  a  wave 
flies  through  the  body,  but  the  wave  differs  in  its  character. 
In  the  pool,  the  wave  is  only  on  the  surface  of  the  water; 
but  in  the  timber  it  is  all  through  it ;  every  particle  of  the 
timber  strikes  against  every  other.  If  we  took  a  sphere  of 
timber  or  of  metal,  and  struck  it  in  the  middle,  the  waves 
would  run  through  all  parts  of  it,  and  give  a  jar  over  the 
whole  surface.  Now,  an  earthquake  is  a  jar  or  wave  of 
just  this  sort  that  moves  through  the  earth.  It  may  be 
made  in  any  one  of  many  ways.  We  have  seen  that  the 
rocks  under  the  surface  are  often  pressed  strongly  to- 
gether, as  in  the  making  of  mountain  ridges.  As  these 
ridges  rise,  the  rocks  slip  over  each  other,  making  a  jar,  as 
when  we  drag  a  table  over  the  floor  ;  or  they  break,  form- 
ing what  are  called  faults,  which  we  know  cause  jars  and 
tremblings.  When  melted  rock  is  thrown  into  fissures, 
forming  dykes,  the  fractured  rocks  are  struck  as  with  a  great 
hammer  by  the  inrush  of  molten  rock.  When  the  steam 
and  other  matters  that  escape  from  a  volcano  force  their 
way  along  underground,  they  cause  the  rocks  to  expand,  and 
make  sharp  movements,  like  steam-pipes  when  the  hot  vapor 
is  let  into  them.  As  this  heat  dies  away,  the  rocks  contract, 
as  the  steam-pipes  do  when  the  steam  is  shut  off.  In  ail 
these,  and  many  other  ways,  the  earth  is  subject  to  sudden 
blows  that  give  us  earthquakes.  We  will  now  see  more 
closely  how  an  earthquake  behaves.  Let  us  suppose 
that,  in  the  diagram,  the  earthquake  starts  in  some  sud- 
den blow  at  a,  and  runs  in  all  directions  to  the  surface  of 
the  earth,  666;  there  will  be  many  shocks  from  one  jar ; 


138  MOVEMENTS   OF    THE   EARTH'S   SURFACE. 

just  as,  when  we  strike  a  drum-head,  or  twang  a  guitar- 
string,  there  will  be  many  waves  follow  the  one  move- 
ment. These  successive  waves  are  indicated  by  the  lines 
c  c'  c",  etc.  Now,  where  a  man  is  standing  just  over  the 
shock,  at  c,  it  will  come  straight  up  beneath  his  feet,  and, 
if  it  is  strong,  he  will  be  thrown  vertically  up  into  the  air, 
from  a  few  inches  to  many  feet  in  height.  When  he  is 
standing  at  c'  or  c",  he  will  find  his  feet  pulled  forward, 
and  his  body  will  be  thrown  to  the  ground.  If  there  are 
three  buildings,  one  just  over  the  shock,  as  at  c,  and  the 
others  at  <?'  and  c",  that  at  c  will  probably  have  its  walls 


Fig.  64. 
Diagram  showing  Earthquake  Waves. 

left  standing,  but  the  roof  and  floors  will  tumble  into  the 
cellar.  Those  at  c'  and  c"  will  have  the  walls  that  are  at 
right  angles  with  the  shock  thrown  down,  while  the  walls 
parallel  to  the  line  in  which  the  shock  runs  will  probably 
remain  standing. 

Just  as  the  waves  made  by  a  splash  in  a  pool  run  out, 
just  as  the  jar  given  at  one  end  of  a  long  timber  becomes 
feeble  at  the  further  end,  so  earthquake  shocks  wear  out 
in  running  through  the  rocks  of  the  earth.  This  causes 
the  shocks  to  become  more  and  more  feeble  as  we  get 
farther  away  from  the  place  where  they  start. 


EARTHQUAKES.  139 

On  the  land,  the  effects  of  an  earthquake  shock  are  very 
great;  but  in  the  sea  they  are  even  greater.  The  shock 
kills  many  animals  in  the  sea.  We  often  find  the  sea,  near 
where  a  great  earthquake  has  happened,  covered  with  dead 
fishes,  which  have  been  killed  by  the  blow  they  received 
through  the  water.  We  can  imitate  this  by  exploding  a 
small  charge  of  dynamite  below  the  surface.  The  blow  it 
gives  is  just  like  that  which  comes  through  an  earthquake. 
This  blow  also  seems  to  stir  up  the  mud  of  the  sea-floor,  and 
this  mud  kills  many  animals.  Then  the  earthquake  lifts  the 
surface  of  the  sea  over  the  place  where  the  shock  starts,  and 
a  wave  rolls  away  from  this  place  which  may  be  strong 
enough  to  cross  the  widest  oceans,  and  often  rolls  on  the 
land  in  a  prodigious  breaker  sixty  feet  or  more  in  height. 
It  is  this  wave  that  so  often  sends  ships  far  inland,  as 
in  the  earthquakes  of  Lisbon  and  Jamaica.  In  the  earth- 
quake of  1746,  which  ravaged  the  west  coast  of  South 
America,  a  Portuguese  man-of-mar  was  carried  for  a 
distance  of  three  miles  inland,  and  left  stranded,  though 
but  little  injured.  Within  twenty-five  years,  several  ves- 
sels have  met  with  this  strange  fate.  This  great  wave, 
though  without  power  to  harm  the  life  of  the  deep  seas, 
is  very  destructive  to  all  the  creatures  that  live  on  the 
shores,  grinding  them  up,  and  mingling  them  with  the 
mud. 

When  we  look  over  the  history  of  earthquakes,  they 
seem  like  very  cruel  agents  of  destruction.  Next  to  bat- 
tles and  famines,  they  are  the  greatest  life-destroying 
accidents  that  can  befall  man;  and,  among  the  lower 
animals,  they  are,  perhaps,  more  destructive  than  any 
other  sudden  convulsion  of  nature.  But,  when  we  con- 
sider how  slight  and  seldom  are  the  shocks  of  great 
destructive  power,  compared  with  the  great  work  of  lift- 


140 


MOVEMENTS   OF   THE  EARTH'S   SURFACE. 


ing  mountains,  forming  volcanoes,  and  otherwise  maintain- 
ing the  activities  of  the  earth,  we  must  regard  them  as  very 
trifling  accidents,  and  rather  wonder  at  the  slightness  of 
their  effects  than  regard  them  as  unnecessary  convulsions. 
Everywhere,  and  at  all  times  in  the  world,  we  see  such 
destruction  of  individual  life ;  yet  the  life  as  a  whole  goes 
onward  and  upwards  as  steadily  as  if  no  death  came 
about  from  the  working  of  the  great  machinery  of  the 
earth.  The  Power  that  rules  the  world  evidently  does 
not  regard  death  as  an  evil  to  be  avoided ;  everything  is 
made  quickly  to  die,  that  better  life  may  follow  it ;  and,  if 
we  accept  death  as  in  the  order  of  nature,  the  destruction 
of  life  by  earthquakes,  volcanic  outbreaks,  storms,  and  all 
the  other  violences  of  the  earth  need  not  shake  our  faith  in 
the  merciful  plan  of  all  things. 


City  ruiued  by  Earthquake,  with  Landslides. 


CHANGES   IX   THE   SHAPE   OF   SEA  AND  LAND.       141 
LESSON  II. 

CHANGES  IN  THE  SHAPE  OF  SEA  AND  LAND. 

ALTHOUGH  the  continents  are  the  very  firmest  thing  we 
know  in  nature,  although  there  have  been  no  great  changes 
in  the  shape  of  land  and  sea  since  the  earliest  human  his- 
tory, we  must  not  suppose  that  the  lands  endure  very  long 
in  one  shape.  We  know  that  in  the  long  ages  of  the  past 
very  great  changes  have  come  over  them.  All  the  rocks 
that  we  know  in  the  world  have,  except  possibly  some  of 
those  thrown  out  by  volcanoes,  been  formed  on  the  bottom 
of  the  sea,  which  is  in  itself  enough  to  prove  that  all  our 
present  lands  have  been  sea-floors.  We  find  fossil  sea- 
shells  on  the  tops  of  our  highest  mountains,  and  there  is 
hardly  a  place  in  the  world  where  we  are  more  than  a  few 
miles  from  rocks  containing  the  remains  of  some  animals 
that  have  lived  on  the  sea-floor. 

The  changes  in  the  shape  of  the  land  take  place  so 
slowly  that  we  cannot  recognize  many  of  them  within  the 
time  of  human  history;  yet,  along  one  coast,  which  has 
been  known  for  some  hundreds  of  years,  viz.,  that  of 
Sweden  and  Norway,  the  shore  is  in  places  rising  as  fast 
as  three  feet  in  one  hundred  years.  On  the  west  shore  of 
South  America,  during  the  great  earthquake  of  1822,  the 
shore  for  some  hundreds  of  miles  rose  suddenly  by  four 
feet  or  more.  Many  other  cases  of  such  changes  could  be 
mentioned,  but  they  only  show  us  how  slowly  accumulated 
modifications  can  affect  great  changes.  A  few  such  lifts  as 
that  on  the  Chilian  shore  would  greatly  alter  the  form  of 
a  continent,  especially  if  they  took  place  on  a  shore  along 
which  the  water  was  not  very  deep. 


142  MOVEMENTS   OF   THE   EARTH'S   SURFACE. 

Besides  these  alterations  that  come  from  the  up-lifting 
or  down-sinking  of  the  lands,  there  are  slower-going 
changes,  due  to  the  wear  of  the  sea  and  of  the  rivers. 
The  water  that  falls  on  the  country  drained  by  the  Missis- 
sippi wears  away  about  one  foot  of  its  rocks  in  every  seven 
thousand  years,  and  bears  the  waste  into  the  sea  to  form 
new  rocks  on  the  sea-floor.  Taking  all  the  river-basins  of 
the  world,  or,  in  other  words,  about  all  the  surface  of  the 
land,  we  have  an  average  down-wear  of  about  one  foot 
in  three  or  four  thousand  years.  This  seems  slow;  yet, 
when  we  consider  that  in  the  life  of  the  earth  a  thousand 
years  is  but  as  a  day,  or,  better,  an  hour  in  our  own  lives, 
it  is  really  a  rapid  wear. 

Then  the  sea  too  does  its  work  of  calling  back  the  lands 
to  its  depths.  Beating  against  the  shore,  it  undermines 
cliffs  and  grinds  their  fragments  to  powder,  which  the  cur- 
rents easily  bear  away  into  the  depths.  When  the  coast  is 
not  faced  with  very  hard  rocks,  it  often  cuts  back  at  the 
rate  of  several  feet  a  year.  In  England,  for  instance, 
whole  townships,  that  once  bore  many  villages,  now  lie 
buried  beneath  the  sea. 

This  work  of  wearing  away  the  rocks  is  mainly  due  to 
the  action  of  the  sun's  heat.  It  sets  in  motion  the  winds 
that  raise  the  sea  waves,  and  it  fills  the  winds  with  water 
that  falls  as  rain ;  but,  though  it  is  a  work  of  destruction, 
it  is  also  a  work  of  preparation  for  lands  that  are  in  time 
perhaps  to  be  lifted  above  the  sea  in  their  turn  to  bear  life. 
The  most  important  effects  of  these  changes  of  the  lands 
are  found  in  their  action  on  the  destruction  of  life  over 
the  earth,  and  in  the  course  of  the  sea-currents,  those  great 
carriers  of  heat  from  one  part  of  the  earth's  surface  to 
another.  We  can  best  understand  these  effects  by  con- 
sidering what  would  happen  if  the  Isthmus  of  Darien, 


CHANGES   IN   THE   SHAPE   OP   SEA  AND   LAND.       148 

which  is  but  a  slender,  low  bit  of  land,  were  to  be  deeply 
submerged  beneath  the  sea.  The  animals  now  living  in 
the  sea-waters  on  either  side  of  this  isthmus  are  very 
different  from  each  other,  hardly  a  species  being  found 
both  in  the  Caribbean  Sea  and  in  the  Pacific  Ocean.  If 
the  isthmus  were  buried  beneath  the  sea,  these  animals  of 
the  two  seas  would  be  brought  into  contention  with  each 
other.  Many  animals  now  limited  to  the  Atlantic  waters 
would  extend  into  the  Pacific,  and  many  unknown  in  the 
Atlantic  would  destroy  those  from  the  Pacific  waters.  Many 
of  the  weaker  kinds  would  be  destroyed  by  their  stronger 
enemies,  and  in  a  few  years  the  life  in  either  ocean  near 
the  isthmus  would  be  greatly  changed. 

If  the  down-sinking  in  the  Central  American  district 
were  carried  so  far  as  to  lower  the  northern  part  of  South 
America  beneath  the  sea,  converting  it  either  into  open 
water  or  into  an  archipelago,  then  the  great  current  that 
becomes  the  Gulf  Stream  would  no  longer  flow  into  the 
northern  Atlantic,  but  would  pass  through  this  gap  into 
the  Pacific  Ocean.  The  result  of  this  would  be  that 
northern  Europe  and  the  most  of  the  United  States  would 
become  too  cold  for  the  life  of  man,  while  the  tropical 
regions  would  have  their  heat  increased.  This  instance 
will  give  an  idea  of  the  effects  that  may  come  from  lower- 
ing lands  beneath  the  sea. 

Now  let  us  turn  to  Asia,  and  imagine  what  would  be 
the  effect  if  the  string  of  islands,  that  nearly  connect  that 
continent  with  Australia,  were  to  rise  higher  above  the  sea, 
so  that  the  two  continents  were  connected  by  a  continuous 
land  bridge.  In  this  case  the  effects  would  be  these,  viz. : 
the  currents  of  warm  water  that  now  pass  from  the  Pacific 
Ocean  to  the  Indian  Ocean,  through  the  straits  between 
these  islands,  would,  when  barred  out  from  the  Indian 


144  MOVEMENTS    OF    THE   EARTH'S    SURFACE. 

Ocean,  turn  northward  and  southward  towards  either 
pole,  carrying  more  warmth  to  the  cold  regions  of  the 
earth  and  diminishing  the  heat  of  the  tropics.  The  con- 
tinent of  Australia  has  hardly  any  quadrupeds  except 
creatures  akin  to  our  opossums,  such  as  the  kangaroos 
and  the  like,  animals  that  carry  their  young  about  in 
pouches.  Of  these  animals,  there  are  over  one  hundred 
species  living  on  that  land.  All  these  creatures  are  much 
weaker  than  the  quadrupeds  of  Asia.  As  soon  as  this 
bridge  across  to  Asia  were  formed,  the  tigers,  leopards, 
and  other  beasts  of  prey  would  pass  south  to  Australia, 
and  quickly  exterminate  the  kangaroo  tribe,  while  their 
place  would  be  taken  by  the  stronger  or  fleeter-footed 
elephants,  buffaloes,  and  deer  from  Asia. 

We  know  very  well  that  just  such  changes  of  level  of 
sea  and  land  as  we  have  imagined  to  occur  in  these  isth- 
muses and  archipelagoes  of  America  and  Asia  have  very 
often  happened  in  the  history  of  the  earth,  so  it  is  fair  to 
presume  that  they  may  happen  in  the  future. 

It  is  hard  to  conceive  this  constant  up-rising  and  down- 
sinking  of  the  shore  ;  but,  if  we  will  consider  the  matter, 
we  shall  see  how  it  must  often  happen.  The  shrinking  of 
the  earth's  interior,  from  the  constant  cooling,  is  constantly 
causing  its  surface  to  wrinkle,  deepening  the  sea-troughs 
and  lifting  the  lands  into  the  air.  The  rivers,  the  sea- 
waves  and  the  tides  are  always  cutting  the  land  down 
to  the  sea  level.  Broad  surfaces  of  the  sea-floor  in  the 
great  oceans  are  sometimes  sinking,  which  serves  to  draw 
the  water  away  from  the  other  seas,  lowering  the  level 
of  the  shores  :  again  they  are  rising,  causing  the  waters 
to  rise  along  all  the  sea-coasts  in  the  world.  When  a 
glacial  period  comes,  a  great  deal  of  the  water  which  now 
is  in  the  seas  is  taken  out  and  heaped  as  ice  on  the  lam? 


CHANGES   IN   THE   SHAPE   OF   SEA   AND   LAND.       145 

about  ihe  poles,  and  this  lowers  the  level  of  the  sea; 
when  the  glaciers  melt,  this  water  is  returned  to  the 
deep,  raising  its  level  again.  Thus  we  see  that  there  are 
abundant  reasons  for  a  change  in  the  height  of  the  sea 
along  the  lands. 

These  changes  do  not  seem  ever  to  destroy  any  of  the 
continents.  From  time  to  time  their  shapes  change,  but 
the  greater  lands  seem  to  have  been  constantly  growing 
ever  since  the  earliest  times  in  the  earth's  history. 


Stages  of  Growth  of  North  America. 


CHAPTER   VIII. 


THE  PLACE  OF  ANIMATED   THINGS  IN  THE   WORLD. 

LESSON   I. 
THE  WORK  OF  LIFE  ON  THE  EARTH. 

A  T  first  sight,  it  may  not  seem  to  the  reader  that  the 
-£^-  animals  and  plants  of  the  world  have  any  very  close 
relation  to  its  structure,  —  that  they  have  any  sufficient 
claim  to  our  attention  when  we  are  considering  the  geo- 
logical history  of  our  earth.  This,  indeed,  was  the  old 
way  of  looking  at  the  realm  of  animated  nature ;  but,  the 
more  we  know  of  the  earth's  life,  the  more  clearly  we 
perceive  that  this  life,  both  inorganic  and  organic,  is  so 
bound  up  together  that  it  is  all  one  in  its  work. 

The  life  of  the  world  came  out  of  the  earth  by  laws 
which  we  do  not  understand.  Every  creature  exists  by  fit- 
ting itself  to  the  physical  forces  about  it,  and  when  it  dies 
its  dust  goes  back  to  the  soil.  As  far  as  its  bodily  parts  are 
concerned,  each  creature  in  the  world  is  but  a  bit  of  earth 
that  has  become  for  the  moment  filled  with  the  forces  of 
life.  All  the  work  of  its  body  is  determined  by  laws  of  the 
earth's  matter  from  which  its  body  is  formed,  and  of  which 
it  always  remains  a  part. 

The  force  that  impels  these  animated  things  is  derived 
from  their  food ;  which,  in  the  plants,  is  either  the  mineral 
matter  of  the  soil  and  the  carbon  in  the  air,  or,  in  the 
case  of  the  animals,  it  is  the  vegetable  kingdom  that  sup- 


THE   WORK   OF   LIFE   ON   THE  EARTH.  147 

plies  the  food  directly  in  the  herbivora,  or  at  second  hand, 
as  in  the  carnivora.  This  force  is  given  to  the  plants  by 
the  action  of  the  sun's  heat ;  by  it  the  plants  separate  the 
carbon  from  the  atmosphere,  and  build  into  their  bodies 
the  mineral  substances  obtained  through  their  roots. 
These  things  the  plants  consume,  and  obtain  thereby  the 
solar  force  that  the  plants  built  into  their  structures. 
In  this  way  we  may  say  that  plants,  and  the  animals 
which  they  support,  owe  their  life  to  the  same  force  that 
sets  the  winds  or  the  rivers  in  motion. 

We  should  notice,  also,  that  the  animal  and  vegetable 
life  of  the  world  plays  a  very  large  part  in  the  working 
of  the  earth's  machinery.  The  land  plants  protect  the 
lands  from  the  rain,  which  would  rapidly  wear  away  their 
surfaces  but  for  the  covering  the  plants  afford.  The  car- 
bonic acid  which  these  decaying  plants  furnish  to  the 
water  give  it  a  great  power  of  dissolving  substances  of 
many  kinds,  and  so  aids  in  the  formation  of  mineral  de- 
posits and  the  excavation  of  caves,  as  we  have  already 
seen.  Plants  and  animals  furnish  a  vast  deal  of  material 
for  the  formation  of  rocks.  More  than  half  the  rocks  on 
the  earth's  surface  owe  their  formation,  in  whole  or  in 
part,  to  the  action  of  animal  or  plant  life.  All  our  coals, 
bituminous  slates,  and  limestones  are  essentially  the  work 
of  the  living  things  of  past  times,  and  the  greater  part  of 
our  sandstones  and  other  rocks  are  partly  their  work. 

We  should  also  see  that  the  greatest  work  of  the  earth, 
from  ancient  ages,  has  been  to  afford  the  place  on  which, 
as  on  a  theatre,  this  life  has  played  its  part.  We  find  the 
most  wonderful  proof  of  the  earth's  perfection  in  the  fact 
that  for  a  time,  so  long  that  our  imaginations  are  too 
weak  to  consider  it,  it  has  been  so  well  ordered  that  no 
convulsions  have  prevented  the  animals  and  plants  from 


148      THE   PLACE   OF  ANIMATED   THINGS   IN   THE  WORLD. 

steadily  going  forward  in  their  development.  Ten  miles 
beneath  the  surface,  there  is  a  heat  so  great  that  no  life 
could  bear  it ;  ten  miles  above,  a  cold  so  intense  that,  if  it 
should  come  to  the  earth,  nearly  all  created  things  would 
immediately  die.  Yet  for  ages  the  balance  has  been  so 
preserved,  and  the  temperature  of  the  earth  has  remained 
so  near  what  it  is  at  present,  that  these  sensitive  living 
creatures  have  not  been  killed,  but  have  prospered  from 
age  to  age. 

In  this  way  we  perceive  the  intimate  relations  between 
life  and  the  world  it  inhabits ;  we  see  that  even  the  brief 
and  general  view  of  the  earth  which  we  are  now  taking 
would  be  too  incomplete  without  at  least  a  glance  at  tht 
history  of  animals  and  plants. 


DIFFERENCE  AND  RELATIONS  AMONG  LIVING  BEINGS.      149 

LESSON  II. 

DIFFERENCE  AND  RELATIONS   AMONG  LIVING  BEINGS. 

WHEN  we  look  around  on  the  beings  that  make  up  the 
kingdom  of  animated  things,  —  the  plants  and  animals  of 
the  world,  —  we  easily  see  that  they  are  in  many  ways  akin 
to  each  other.  First,  we  see  that  they  all  have  some  com- 
mon qualities.  They  are  alive,  they  grow,  they  reproduce 
their  kind,  and  in  due  time  they  die,  —  actions  which 
separate  them  widely  from  the  mineral  kingdom.  Then 
we  see  that  the  animals  are  pretty  distinctly  separated 
from  the  plants  by  the  fact  that  besides  their  life,  growth, 
etc.,  features  which  are  common  to  both,  animals  have 
sensations,  and  show  even  in  the  lowest  forms  signs  of 
something  like  will  in  their  motions. 

Among  animals,  we  notice  a  great  many  different  degrees 
of  kinship.  We  see,  for  instance,  that  all  our  common  four- 
footed  animals  are  akin  to  each  other.  Bulls,  sheep,  deer,  and 
other  horned  animals  are  closer  related  to  each  other  than 
they  are  to  pigs,  elephants,  or  horses.  Crayfishes,  lobsters, 
spiders,  and  insects  are  evidently,  by  their  outside  jointed 
structure,  more  like  each  other  than  they  are  to  our  back- 
boned  animals.  If  we  compare  our  own  bodies  with  the 
lower  animals,  we  see  at  once  that  our  nearest  animal  kin- 
dred are  among  the  ordinary  quadrupeds.  This  matter  of 
relationship  may  be  by  study  carried  much  further,  for  we 
find  that  all  animals  are  related  to  one  another  in  varying 
degrees.  A  great  part  of  the  study  that  naturalists  have 
given  to  living  things  has  had  for  its  object  the  determin- 
ing of  those  relations  that  exist  among  them.  The  result 
is  that  we  find  that  these  relationships  may  be  expressed 


150      THE   PLACE   OF   ANIMATED   THINGS   IN   THE  WORLD. 

by  what  is  called  a  system  of  classification.  At  first  sight, 
this  scheme  of  classification  looks  very  complicated;  but, 
if  we  look  at  it  carefully,  we  see  that  it  rests  on  very  sim- 
ple principles.  A  clear  understanding  of  these  principles 
may  be  had,  if  we  take  some  other  objects  than  animals 
and  plants,  and  apply  a  system  of  classification  to  them. 

For  this  illustration,  let  us  take  the  contrivances  made 
by  man  for  measuring  time.  There  have  been  many  differ- 
ent plans  of  accomplishing  this  end,  which  rest  on  the  fol- 
lowing plans  of  working.  First,  we  have  the  ancient  water 
clocks,  where  time  was  measured  by  allowing  water  to 
drop  out  of  a  vessel  through  a  small  hole.  A  familiar  in- 
stance of  this  mechanism  is  the  sand-glass,  where  sand, 
slipping  through  a  narrow  opening,  measures  the  time.  In 
these  there  is  the  common  plan  of  having  some  particles 
of  water  or  sand  slip  through  a  hole  under  the  influence 
of  the  earth's  attraction.  They  differ  in  the  way  of  car- 
rying out  the  plans  in  the  two  machines ;  or,  we  may  say 
that  there  is  one  plan  of  structure  in  these  machines,  and 
two  divisions,  which  we  may  conveniently  term  classes  of 
structure  under  the  plan.  Then  we  have  the  sun-dials, 
where  there  is  a  very  different  plan,  and  two  classes  of 
methods  of  carrying  out  the  plan.  One,  when  the  gnomon, 
or  part  that  casts  the  shadow,  is  fixed ;  another,  when  it  is 
attached  to  a  magnetic  compass,  so  that  it  may  set  itself 
at  any  time.  Examining  the  structure  of  fixed  dials,  we  find 
that  sometimes  they  are  horizontal,  sometimes  vertical,  as 
in  those  that  are  placed  against  a  wall.  To  these  divisions 
we  may,  as  before,  give  any  name  we  choose,  but  for  con- 
venience we  may  term  them  orders  under  the  class  of 
fixed  dials.  Looking  more  closely  at  these  dials,  we  find 
yet  further  differences  under  each, — some  of  the  horizontal 
dials  are  set  up  in  columns,  and  some  are  placed  on  the 


DIFFERENCE  AND  RELATIONS  AMONG  LIVING  BEINGS.     151 

pavement.  These  differences  we  may,  for  convenience, 
term  families  under  the  order  of  horizontal  fixed  dials. 
We  may  go  still  further  in  our  division.  In  some  cases, 
we  see  that  the  figures  denoting  the  hours  are  printed  on 
the  dial ;  in  other  cases,  they  are  cut  into  its  substance. 
These  differences  we  may  denote  by  the  name  genus,  and 
we  would  make  two  genera  of  dials  in  each  of  the  two 
families.  By  careful  study,  we  should  find  that  many 
such  genera  could  be  made.  Finally,  our  examination 
brings  us  to  groups  of  sun-dials  which  are  all  so  alike  that 
we  cannot  perceive  any  constant  differences  among  them. 
They  are  of  about  the  same  size,  shape,  color,  etc.  We 
may  even  suppose  that  they  came  from  the  same  factory. 
These  groups  we  will  term  species. 

We  can  take  the  same  course  with  the  other  and  more 
varied  plan  of  time-measurers,  —  clocks  and  watches.  We 
shall  find  these  classes,  orders,  families,  genera,  and  species 
just  as  we  have  seen  that  they  exist  in  sun-dials,  only  it 
takes  more  time  and  more  study  of  their  mechanism  to 
make  them  out. 

This  system  of  classification  can  be  applied  to  a  great 
many  other  structures;  indeed,  to  all  forms  of  human 
contrivances  where  men  have  made  many  inventions  all 
working  towards  one  result.  The  reader  can  see  that  in 
instruments  for  aiding  locomotion,  such  as  ships,  wagons, 
balloons,  etc.,  or  in  contrivances  for  giving  power,  such  as 
windmills,  steam  mills,  water  mills,  etc.,  or  implements  of 
war,  such  as  armor,  arms,  javelins,  spears,  swords,  guns, 
etc.,  the  same  system  of  classification  can  be  made. 
It  will  be  more  profitable  for  the  reader  to  work  these 
out  for  himself  than  for  them  to  be  described  here ;  for 
the  only  aim  of  this  classification  of  human  products  is  to 
show  the  principle  of  the  classification  which  is  applied  to 
natural  objects,  which  otherwise  is  hard  to  understand. 


152      THE   PLACE   OF   ANIMATED   THINGS   IN   THE   WORLD. 

When  we  apply  this  principle  of  denning  relationship  or 
likeness,  according  to  its  degrees,  to  animals  and  plants, 
we  find  that  it  leads  us  to  essentially  the  same  result  as 
when  it  is  applied  to  human  contrivances.  There  is  al- 
ways something  like  a  plan  which  naturalists  sometimes 
call  a  type ;  different  ways  in  which  the  plan  is  carried 
out,  called  classes;  peculiar  complications  of  it,  termed 
orders  ;  under  these  orders,  variations  of  the  general  shape 
to  suit  different  conditions,  called  families;  still  other 
subordinate  divisions,  based  on  details  of  structure,  called 
genera;  and  finally,  the  last  division  that  we  can  make, 
which  is  commonly  termed  a  species.  All  these  divisions 
rest  upon  differences  in  the  ways  in  which  animals  adapt 
themselves,  by  their  peculiarities,  to  the  needs  of  their  life. 

Among  animals  these  divisions  are  clearer  and  more 
numerous  than  among  plants,  for  the  reason  that  animals 
have  more  definite  and  numerous  results  which  they  seek 
to  attain  than  have  the  plants. 

Among  animals,  naturalists  recognize  several  different 
plans  of  structure.  The  differences  are  in  the  general 
ways  in  which  the  animals  are  built.  These  differences 
may  be  compared  to  the  various  sorts  of  time-keepers. 
In  time-keepers  there  is  one  object,  viz.,  to  divide  time 
into  intervals ;  but,  among  animals,  the  creatures  must 
do  a  number  of  tasks:  they  must  nourish  themselves, 
protect  themselves  from  enemies,  reproduce  their  kind,  — 
all  of  which  the  plants  do  as  well,  —  but  above  all  they 
must  have  some  mechanism  of  sensation,  some  fitness  for 
the  work  of  intelligence,  however  low  that  intelligence 
may  be. 

These  plans  of  building  animal  structures  for  their 
many  uses  are  five  or  six  in  number.  The  protozoa,  the 
radiates,  —  which  group  is  sometimes  divided  into  two, — 


DIFFERENCE  AND  KELATIONS  AMONG  LIVING  BEINGS.     153 

the  articulates,  the  mollusks,  and  the  vertebrates.  Some 
naturalists  have  made  more  than  these  divisions,  but 
those  given  above  are  the  most  clearly  to  be  seen.  In  each 
of  these  groups  there  are  two  or  more  classes ;  in  each  class 
several  orders;  in  each  order  many  families;  and  under 
each  family  many  genera ;  under  each  genus  many  species 
are  ranged.  It  is  not  possible  for  us  to  trace  these  divisions 
here, — that  would  be  a  great  task, — but  only  to  give  the 
reader  some  idea  of  the  nature  of  the  classification  among 
animals,  for  that  has  often  to  be  set  before  the  mind  of 
any  one  who  considers  organized  beings.  To  make  the 
matter  clearer,  we  will  consider  the  way  in  which  a  natu- 
ralist looks  at  an  animal  when  he  is  classifying  it.  For 
this  purpose  we  will  take  a  common  honey-bee  as  an  ex- 
ample of  the  work. 

First,  we  notice  that  the  bee  is  a  member  of  the  organic 
kingdom,  because  it  has,  in  common  with  the  other  ani- 
mals and  plants,  the  powers  of  nutrition,  growth,  repro- 
duction, etc.,  —  qualities  that  belong  to  all  this  group  of 
natural  objects.  Second,  that  it  belongs  to  the  group  of 
animals,  because  it  has  the  means  of  perceiving  sensa- 
tions, and  a  share  of  that  quality  of  mind  that  separates 
all  animals  from  plants.  Third,  that  it  is  an  articulate 
animal,  because  its  body  is  built  on  the  plan  of  many 
ring-like  segments  placed  one  behind  the  other,  like  the 
worms,  lobsters,  or  cray-fishes.  Fourth,  that  it  belongs 
to  the  class  of  insects,  because,  in  common  with  all  the 
insects,  it  has  three  pairs  of  jointed  legs,  each  pair  belong- 
ing to  one  of  the  middle  segments  of  the  body,  a  separate 
movable  head,  and  an  abdomen  divided  from  the  parts 
that  bear  the  legs.  Fifth,  it  belongs  to  that  particular 
group  of  the  insects  called  hymerioptera  or  membranous 
wings,  because  it  has  four  wings,  not  covered  with  scales, 


154      THE  PLACE   OF   ANIMATED   THINGS   IN  THE  WOELD. 

as  in  the  group  of  butterflies,  but  made  of  an  easily-folded, 
cloth-like  substance,  as  well  as  certain  peculiarities  of  the 
jaws  which  fit  them  for  very  varied  work.  Sixth,  it 
belongs  to  the  special  family  of  bees,  and  is  separated 
from  the  wasps,  the  saw-flies,  and  the  ants,  by  its  peculiar 
solid,  compact  form,  which  enables  us  in  a  moment  to  see 
that  all  the  bees  belong  together.  Seventh,  it  belongs  to 
the  genus  of  bees,  because  of  the  special  structures  about 
the  mouth,  etc.,  which  are  not  present  in  other  members 
of  the  family.  Eighth  and  last,  it  belongs  to  the  honey- 
bee species,  because  it  has  the  precise  form,  the  color,  and 
the  habits  that  mark  its  kindred.  Thus,  by  eight  steps  of 
division,  we  place  this  creature  so  as  to  show  the  greater 
differences  between  itself  and  the  other  living  things. 
This  process  we  take  in  classification  with  any  animal  or 
plant. 


CHAPTER   IX. 


A   SKETCH  OF  THE  EARTH'S   ORGANIC  LIFE. 


LESSON  I. 
LINES  OF  ADVANCE   IN  ORGANIC  CREATURES. 

TTTE  have  already  glanced  at  a  part  of  the  machinery 
^  *  by  which  the  earth  carries  on  its  physical  life.  We 
have  been  able  to  look  only  at  the  merest  outlines  of  this 
work.  Yet  we  have  seen  that  the  earth  is  not  a  place 
where  mere  accidents  contend  against  others,  but  that  its 
physical  work  goes  on  with  a  stately  order ;  that  even  its 
most  violent  activities,  the  volcano,  the  earthquake,  the 
lifting  of  the  lands  from  the  sea,  and  the  mountains  upon 
the  land,  are  all  so  accomplished  that  the  alteration 
does  net  break  the  harmony  of  the  whole  work,  but 
rather  contributes  to  its  perfection.  We  have  now  to 
consider  the  second  and  higher  form  of  the  earth's  life,  — 
that  which  exists  in  things  which  we  call  living,  —  in  ani- 
mals and  plants.  The  lower  or  physical  life  of  the  earth 
shows  us  matter  in  the  control  of  laws  that  shape  it  into 
the  lands,  the  mountains,  in  sea  or  air,  but  leaves  it 
without  sensibility,  without  power  to  renew  itself.  Moun- 
tains or  crystals,  and  other  inanimate  things  are  brought 
to  their  shape  and  pass  away  into  the  waters  without 
helping  themselves  in  any  way.  In  this  regard  they  are  in 
strong  contrast  with  living  beings.  All  plants  and  ani- 
mals grow  from  within  themselves  by  processes  that  make 


156        A    SKETCH   OF    THE    EARTH'S    ORGANIC    LIFE. 

them  living.  They  can  all  multiply  their  kind.  In  these 
respects  they  are  strongly  contrasted  with  all  the  so-called 
lifeless  part  of  the  earth,  which,  though  in  a  true  sense 
living,  exists  in  other  ways.  Every  animal  and  every 
plant  feeds  in  some  way  or  other ;  it  can  take  in  the  mat- 
ter from  the  world  outside  of  its  body,  and  by  changing 
the  chemical  shape  of  this  matter  it  can  accomplish  two 
ends:  it  can  take  the  matter  itself,  to  build  its  body  or  to 
reproduce  its  kind,  and  it  can  take  the  force  that  exists  in 
the  matter,  and  use  it  for  its  own  purposes,  —  to  move  its 
body  with,  or  to  carry  on  the  circulation  of  its  blood,  or 
any  other  of  many  uses.  In  this  they  may  be  com- 
pared with  a  steam  engine.  For  instance,  when  plants 
.take  in  carbonic  dioxide,  which  consists  of  one  part  of 
carbon  and  two  parts  of  oxygen  bound  together,  they 
separate  the  two  elements,  build  the  carbon  into  their 
bodies,  and  throw  the  oxygen  into  the  air.  To  effect  this 
change,  they  make  use  of  the  light  and  heat  of  the  sun ; 
for  it  takes  a  certain  amount  of  force  to  separate  these 
two  elements.  When  an  animal  eats  the  plant,  it  burns 
part  of  this  carbon  in  its  lungs,  by  bringing  it  in  contact 
with  the  air,  and  thereby  'gets  a  good  deal  of  force  to  use 
in  the  various  movements  of  its  body.  It  is  this  power  of 
taking  a  force  from  the  outside  world,  and  using  it  to  sus- 
tain all  sorts  of  activities,  that  separates  the  animal  and 
vegetable  world  from  the  lower  life  of  the  earth,  and  makes 
them  a  kingdom  by  themselves.  Because  of  this  peculi- 
arity, there  can  be  no  passage  from  the  mineral  to  the 
living  world. 

Animals  and  plants  appear  to  have  begun  in  a  very 
ancient  stage  of  the  earth's  history ;  we  do  not  know  just 
where,  when,  or  how  the  beginnings  were  made ;  for  the 
ancient  history  of  life  has  been  lost  to  us,  through  the 


LINES   OF   ADVANCE   IN   ORGANIC    CREATURES.       157 

changes  that  the  rocks  have  undergone,  which  have  de- 
stroyed all  the  fossils  they  ever  may  have  contained. 
These  earliest  forms  were  doubtless  of  a  very  simple 
structure. 

The  lowest  organized  beings  we  know  have  many  of  the 
features  both  of  animals  and  plants.  They  are  little  bits 
of  a  jelly-like  substance,  having  no  distinct  form,  no  parts 
of  the  body  adapted  to  any  special  uses,  such  as  eating, 
digesting,  motion,  etc.,  as  have  our  higher  animals.  From 
some  such  simple  foundation  of  life  all  beings  seem  to  have 
sprung,  through  the  action  of  laws  that  we  do  not  yet 
fully  understand.  We  can  see  one  kind  coming  after  the 


.  65.    Rhizopods. 

other  and  out  of  the  other,  as  we  go  through  the  records 
of  the  rocks  from  the  earliest  days  to  the  present  time, 
but  we  cannot  see  just  how  the  change  from  one  kind  to 
another  is  effected.  Very  early  in  the  history  of  the 
world,  it  is  clear  that  these  two  kinds  of  beings,  plants 
and  animals,  were  begun. 

The  lower  plants  were  probably  seaweeds.  The  plan  on 
which  their  structure  was  built  made  beings  suited  for 
taking  carbonic  dioxide  gas  out  of  the  sea-water,  which 
contains  a  little  of  this  gas,  and  for  building  its  carbon 
into  the  body  of  the  creature.  They  also  took  a  number 


158        A  SKETCH   OF  THE  EARTH'S   ORGANIC   LIFE 

of  other  substances  from  the  water.  There  were  in  them 
no  roots,  and  they  differed  from  distinct  animals  in  having 
no  arrangement  for  sensation.  This  is  the  really  strong 
difference  between  animals  and  plants.  Plants  work  to 
make  structures  that  get  along  without  any  sensations, 
while  animals,  from  the  first,  and  always,  provide  for  this 
work  of  receiving  impressions  from  the  outer  world.  Ani- 
mals, even  the  lowest,  also  have  means  of  making  voluntary 
movements,  which  either  help  them  in  feeding  alone,  or, 
when  they  are  not  fixed  as  by  a  stem  to  some  solid  body, 
enables  them  to  move  about  at  will.  Some  low  plants,  and 
the  seed  of  many  plants,  have  means  of  moving  that  at  first 
sight  look  like  those  of  animals ;  but  they  are  plainly 
involuntary  organs,  and  not  connected  with  any  capacity  of 
recurring  nervous  sensations  nor  to  be  compared  with  the 
motive  parts  of  true  animals. 

When,  from  the  lowest  forms  of  these  beings  we  pass 
upward  to  the  higher,  we  find  that  in  plants  the  following 
objects  are  sought  to  be  accomplished.  The  structure  is 
arranged  so  as  to  give  a  solid  stem  and  branches,  and 
to  contain  many  separate  individuals  in  one  community. 
The  work  of  leaves  is  separated  from  the  rest  of  the 
plant,  and  the  roots  are  inverted,  which  enable  the  plant 
to  draw  a  certain  share  of  its  nourishment  from  the 
ground.  Especially,  it  can  find  water  there,  which  would 
often  be  unattainable  in  the  air.  While  the  plants  remain 
water  creatures,  they  do  not  need  their  roots :  it  is  only 
when  they  come  to  dwell  on  the  land  that  their  roots  be- 
come developed.  In  the  water  they  found  all  they  needed 
for  their  life  without  these  appliances. 

These  steps  lead  us  up  from  the  simplest  seaweeds,  which 
have  nothing  that  we  can  fairly  call  leaves,  stems,  or  roots, 
through  the  higher  seaweeds,  where  the  stem  becomes  dia- 


LINES   OF   ADVANCE   IN   ORGANIC   CREATURES.      159 

tinct  from  the  leaves,  through  the  mosses  and  lichens,  the 
ferns,  the  palms,  the  pines,  to  our  oaks  and  other  familiar 
trees. 

In  this  succession  of  forms,  the  plant  contrives  to  sepa- 
rate its  parts  into  the  roots,  that  gather  food  from  the 
soil,  the  stem,  which  supports  the  upper  part  of  the  body 


Fig.  66.    Plants  with  and  without 
Roots  and  Stems. 


and  keeps  a  connection  with  the  root,  and  the  branches 
which  support  the  leaves  and  flowers.  At  first,  the  stem 
and  branches  have  no  distinct  bark,  and  they  grow  by  ad- 
ditions made  throughout  the  mass  of  the  wood ;  but  in 


Fig.  67.    Endogens  and  Exogens. 

time  they  devise  a  way  of  growing  only  on  the  out  or 
bark  side,  the  inner  part  of  stem  and  branches  being  very 
solid,  so  as  to  serve  for  support,  while  the  sap  is  carried  in 


160        A   SKETCH   OF   THE  EARTH'S   ORGANIC   LITE. 

the  bark  alone,  and  the  solid  central  wood  forms  a  bet- 
ter support.  This  contrivance  enables  the  plants  to  have 
smaller,  stronger  branches,  and  their  trunks  can  carry  more 
top  burden  of  twigs  and  leaves. 

In  its  perfected  form,  the  tree  consists  of  many  separate 
individuals,  —  the  buds,  united  together  by  their  common 
property,  the  branches  and  trunk,  while  the  roots  below 
do  the  work  of  separating  the  mineral  substances  from 
the  water  that  dissolves  them,  bearing  them  in  the  sap  up 
to  the  leaves. 

But  the  changes  that  take  place  in  the  general  form  of 
the  plant  are  only  a  small  part  of  the  whole  change  that 
occurs  in  the  ascent  from  the 
lower  to  the  higher.  These 
are  so  numerous  that  we  will 
not  try  to  trace  them.  There 
is  only  one  other  that  needs 
our  attention.  In  the  lower 
kind,  we  have  only  one  indi- 
vidual in  one  plant.  As  we 
go  higher,  many  individuals 
come  to  be  associated  to- 
gether, as  in  our  common 

Fig.  68.  Single  and  Compound  Plants.  trees_      An  oak?    for  example> 

is  really  an  association  of  many  different  plants,  each  bud 
being  a  distinct  plant,  all  of  them  uniting  in  the  work  of 
building  the  stem,  branches,  and  roots,  which  are  the  com- 
mon property  of  the  association.  This  careful  bringing 
together  of  many  distinct  individuals  in  one  community  is 
a  peculiarity  of  the  higher  plants. 

These  changes  have  for  their  purpose  the  better  life  of 
the  individual  plant.  There  are  others,  and  more  impor- 
tant, which  are  contrived  for  the  good  of  the  seed.  The 


LINES    OF   ADVANCE  IN   ORGANIC    CREATURES.       161 

lowest  plants  have  very  small  and  simple  seeds,  and  noth- 
ing that  can  fairly  be  called  a  flower.  The  spores,  as  these 
tiniest  forms  of  seeds  are  called,  are  very  small  and  very 
numerous.  They  are  made  on  the  leaves,  as  in  the  ferns. 
In  this  state,  the  seed  has  life  alone  given  it  by  the  parent 
plant.  No  food  is  stored  with  the  germ.  In  the  higher 
plants,  there  is  a  distinct  flower,  made  up  of  a  number  of 
leaves  that  have  changed  their  shape  to  make  the  parts  of 
the  blossom.  This  flower  develops  seeds  of  a  higher 
structure  than  those  of  the  lower  plants.  Around  the 
life-containing  germ  is  gathered  a  supply  of  starch  and 
other  food  intended  to  support  the  young  plant  in  its 
earliest  stages  of  growth.  In  this  way,  the  parent  gives 
something  of  its  strength  to  help  the  offspring  in  its 
period  of  infancy. 

These  changes  from  the  lower  to  the  higher  plants  are 
slowly  worked  out  in  the  course  of  the  long  ages  of  the 
earth's  history.  Plants  do  not  move  upward  in  their 
structure  with  the  same  speed  as  the  animals ;  still  they 
have  advanced  age  by  age,  and  finally  give  us  our  flowers 
and  fruits.  The  flowers  and  fruits  are  offerings  the  plants 
make  to  the  insects,  birds,  and  other  animals  in  order  to 
get  their  help  in  the  work  of  fertilizing  their  seed,  and  con- 
veying them  to  places  where  they  may  grow.  To  fertilize 
a  seed  in  the  best  way,  it  is  necessary  to  carry  the  pollen  of 
one  plant  to  the  pistil  of  the  flower  that  grows  on  another 
plant.  This  is  done  by  the  insects.  They  are  attracted 
by  the  gay  flowers  and  sweet  odors  of  the  plants,  and  are 
paid  for  their  labor  by  the  honey  and  pollen  they  get  by 
their  visits.  They  go  smeared  with  the  pollen  from  plant 
to  plant,  and  thus,  without  intending  it,  fertilize  the  seed 
in  the  way  best  suited  to  their  needs.  The  fruit,  by  its 
sweetness,  and  the  seeds,  by  their  nourishment,  tempt  the 


162        A   SKETCH   OP  THE  EARTH'S   ORGANIC   LIFE. 

birds  and  beasts  to  eat  them,  and  in  this  way  they  are 
carried  about  and  dropped  in  places  which  will  give  them 
a  chance  to  grow  to  advantage.  Other  seeds,  which  have 
hooks  upon  them,  are  arranged  so  as  to  catch  on  the  fur 
of  animals,  and  so  are  carried  about  until  they  fall  far 
away  from  the  parent  plant. 

There  are  many  other  ways  in  which  the  plants  seek 
the  help  of  the  animal  world ;  but  these  few  examples  will 
serve  to  show  us  how  closely  knit  together  are  these  two 
kingdoms  of  life,  how  they  reckon  on  each  other  for  help 
in  the  struggle  for  existence.  In  this  work,  the  plants  give 
far  more  than  they  receive.  They  give  to  animals  all  their 
food,  for  there  are  no  forms  of  animal  life  that  can  take 
food  directly  from  the  mineral  world.  All  must  come  to 
them  through  the  plant.  In  exchange,  they  receive  from 
the  animals  only  a  little  help  in  the  fertilizing  and  the 
carriage  of  their  seeds.  Even  this  they  pay  for  with  their 
honey,  the  sweetness  of  their  fruits,  or  the  nutrition  of 
their  seed,  so  that  really  the  plant  world  gives  everything 
and  receives  but  a  trifling  recompense. 

The  animal  kingdom  has  an  altogether  different  set  of 
purposes  from  the  plants.  The  animal  form  appears  to  be 
striving  to  make  itself  more  and  more  fitted  to  be  the 
habitation  of  intelligence.  For  this  purpose,  it  needs  to 
be  very  different  from  the  plant.  It  needs,  in  the  first 
place,  to  have  a  system  that  shall  serve  for  the  reception 
of  sensations,  for  the  seat  of  the  intelligence,  and  the 
giving  of  the  commands  of  the  intelligence.  This  is  ac- 
complished by  the  making  of  the  nervous  system,  the 
machinery  of  intelligence,  which  slowly,  as  we  go  higher 
and  higher,  takes  on  a  more  and  more  perfect  character, 
with  eyes,  ears,  the  power  of  taste,  smell,  etc.,  to  give 
communication  between  the  intelligence  and  the  outer 
world. 


LINES   OF   ADVANCE  IN   ORGANIC   CREATURES.      163 

Then  the  animal,  to  be  a  fit  seat  for  intelligence,  needs 
a  variety  of  parts  that  shall  obey  the  will,  organs  for 
grasping,  for  motion  through  the  water  or  air,  or  over  the 
earth.  All  this  is  brought  about  by  the  limbs  in  their 
many  various  shapes,  under  the  intellectual  control. 


164        A   SKETCH   OF   THE  EARTH'S   ORGANIC   LIFE. 


LESSON  II. 

PROTOZOA  AND  RADIATES. 

THE  lines  of  advance  among  animals  are  not  made  in 
one  ascending  path,  as  they  are  among  the  plants.  There 
are  at  least  four  great  groups  of  animals,  each  of  which 
takes  its  own  proper  line  in  the  effort  to  work  out  the 
problem  of  how  to  build  a  structure  fitted  for  the  uses  of 
intelligence.  Most  naturalists,  indeed,  consider  that  there 
are  five  of  these  lines  of  advance.  The  lowest  of  these  five 
is  the  protozoa,  or  animals  of  lowly  life ;  the  simplest  of 


Fig.  69.    Rhizopods. 

these  creatures  generally  appear  to  us  as  mere  masses  of 
jelly,  that  have  no  distinct  mouth  or  stomach,  and  no 
regular  organs  for  moving  the  body.  They  do  not  lay 
eggs,  but  increase  in  numbers  by  dividing  the  mass  of  the 
body,  each  part  being  able  to  set  up  life  for  itself.  These 
forms  are  all  very  small,  —  the  most  of  them,  indeed,  micro- 
scopic in  size  ;  they  are  generally  transparent ;  sometimes 
they  are  as  easy  to  see  through  as  a  bit  of  jelly.  Yet  it 
will  not  do  to  be  too  certain  of  their  simplicity,  for  the 
reason  that,  though  appearing  so  little  complicated,  they 
often  build  structures  of  the  greatest  beauty  and  symmetry. 


PROTOZOA  AND   EADIATES.  165 

Many  species  of  these  protozoa  assemble  themselves  in 
communities,  resembling  the  communities  of  individuals 
that  make  up  an  oak  or  a  pine  tree ;  such,  for  instance, 
are  the  sponges,  which  are  each  made  by  myriads  of  ani- 
mals that  grow  together,  and  by  uniting  their  work,  build 
a  mass  many  thousand  times  as  large  as  the  individual 
animals.  They  all  dwell  in  the  water. 

Higher  in  the  scale  than  the  protozoa  stand  the  radiates; 
these  are  generally  star-like  in  form ;  each  ray  of  the  star 
is  made  up  of  a  set  of  parts ;  in  the  middle  is  a  mouth  and 
stomach,  which  do  the  work  for  all  the  rays.  This  star- 
like  order  of  parts  is  much  like  what  we  have  in  the 


Fig.  70.    Sea  Anemones,  closed  and  partly  opened,  akin  to  Corals. 

plants,  which  generally  show  something  of  a  star-like 
arrangement  of  parts.  They  are  all  water  animals. 

The  lowest  radiates  are  the  corals  and  jelly-fishes; 
these  creatures  generally  are  grouped  together  in  com- 
munities, many  thousands  working  to  build  a  common  sup- 
port. This  gives  them  great  strength ;  while,  if  separated, 
they  would  be  very  weak  animals,  quite  at  the  mercy  of 
the  waves. 

The  next  higher  radiates,  the  crinoids,  are  also  usually 
attached  to  the  bottom  of  the  sea ;  but  they  are  much 
larger  creatures,  and  encased  in  a  solid  shell,  which  stands 


166         A   SKETCH   OF   THE   EARTH'S   ORGANIC   LIFE. 

up  on  a  flexible  stem.     They  are  no  longer  such  simple 

forms  as  their  lower  kinsmen,  the  corals. 

Next  higher,  we  have  the 
I  star-fishes,  which  are  the  first 
animals  that  can  crawl  by 
means  of  something  like  feet. 
They  have  suckers  coming 
from  one  side  of  the  arms, 
that  enable  them  to  move 
along  the  bottom  with  some 
ease.  Still  the  direction  of 
their  movement  is  not  deter- 
mined ;  they  move  quite  as 
Fig.  71.  Sea  Lily.  easily  one  way  as  another. 

Having  nothing  like  a  head,  they  have  no  need  of  a  definite 

direction  of  movement. 

Then  we  have  the  sea-eggs  or  echini,  where  the  animal  is 

condensed  into  a  sphere-like  form ;  and  in  the  highest  of 


Fig.  72.    Holothurian. 

these  radiate  animals  we  find,  for  the  first,  an  animal  that 
moves  in  a  definite  direction.  Although  various  animals 
of  lower  structure  move,  it  is  first  in  the  echini  that  we 
have  this  motion  fixed  in  its  direction.  The  creature  does 
all  in  its  power  to  twist  the  body  into  such  a  shape  that 
the  mouth  may  come  at  the  front  end  of  the  body ;  but 


PROTOZOA  AND   RADIATES.  167 

the  way  in  which  it  is  built  makes  this  a  very  difficult 
thing  to  do.  Finally,  in  the  sea-cucumbers,  or  the  holo- 
thurians,  the  creature  is  turned  over  so  that  it  walks  on  its 
side ;  in  this  way  it  manages  to  use  two  of  its  bands  of 
suckers  as  limbs,  and  the  mouth  is  brought  at  the  advanc- 
ing end  of  the  animal.  These  radiates  give  us  the  first 
series  of  efforts  to  build  a  structure  fitted  for  the  uses  of 
intelligence ;  the  only  structures  out  of  which  they  could 
build  limbs  were  the  soft  suckers  on  the  arms  and  the 
stiff  spines ;  they  do  all  that  can  be  done  with  them,  but 
they  are  not  well  fitted  for  this  work  of  motion ;  besides,  the 
radiate  plan  of  the  body  is 
better  suited  for  a  fixed  than 
for  a  movable  form,  as  we 
see  from  the  fact  that 
plants  are  generally  radi- 1 
ate  in  form.  It  requires  a 
great  deal  of  time  for  these  | 
simple  experiments  of  radi- 
ated animals  to  be  carried 
through  to  their  half-suc- 
cessful end.  The  radiates  Fly.  73.  star-fish, 
are  among  the  earliest  animals  known  to  us,  and  it  is  not 
until  near  the  present  day  that  all  these  experiments  in  loco- 
motion had  been  tried.  The  nervous  system  on  which  more 
than  anything  else  the  fitness  of  the  body  for  the  uses  of  the 
mind  depends,  is  not  even  at  the  end  well  developed  in  the 
radiates ;  yet  it  deserves  to  be  remembered  that  this  system 
did  actually  begin  in  this  group,  and  is  carried  to  a  certain 
state  of  completeness.  We  find  traces  of  it  in  the  jelly-fishes, 
and  it  is  best  shown  in  the  sea-eggs  (echini)  and  the  sea- 
cucumbers  (holothurians) .  It  is,  however,  not  to  be  compared 
with  the  perfection  of  the  same  system  in  the  higher  forms 
of  the  other  higher  groups  of  animals,  as  we  shall  shortly  see. 


168        A   SKETCH   OF   THE   EARTH'S    ORGANIC    LIFE. 

LESSON  III. 

THE    MOLLUSKS. 

THE  next  great  group  of  animals  above  the  radiates  is 
the  mollusks,  familiarly  known  to  us  in  our  oysters,  clams, 
slugs,  snails,  squids,  cuttle-fishes,  etc.  This  group  differs 
widely  from  the  radiates  in  the  plan  on  which  the  body  is 
built.  In  the  radiates,  similar  parts  are  arranged  about  a 
centre  of  growth,  where  the-  mouth  and  stomach  are  situa- 
ted ;  in  the  mollusks,  the  parts  are  placed  on  either  side  of 
a  plane  that  extends  from  the  front  to  the  rear  end  of  the 
body.  The  mouth  is  at  the  anterior  end  of  this  line. 
This  arrangement  of  parts  is  just  what  is  needed  in  the 
animal  body ;  it  makes  motion  possible ;  and  in  this 
motion  the  head  can  go  foremost.  The  nervous  sys- 
tem in  the  mollusks  is  better  built  than  in  the  radiates. 
It  exists  even  in  the  lowest  forms,  and  attains  a  high 
grade  of  perfection  in  the  highest  creatures  of  this  group, 
the  squids,  which  are  really  very  perfectly  adapted  to  the 
uses  of  intelligence.  The  simplest  mollusks  are  akin  to  our 
clams  and  oysters.  In  the  lowest,  the  creature  has  but 
slight  power  of  motion,  often  being  fixed  to  the  bottom 
by  the  shell  or  by  a  sort  of  rope  the  animal  spins.  The 
higher  forms,  like  our  hard  shells  or  the  fresh-water  clams, 
are  able  to  move  by  means  of  a  flesh  projection  called 
the  foot,  that  can  be  pushed  outside  of  the  shell,  and  used 
in  crawling,  like  the  foot  of  a  slug  or  snail.  Our  fresh- 
water clams  or  unios  can  travel  at  the  rate  of  something 
like  fifty  feet  an  hour.  This  is  the  most  successful  walking 
that  has  been  attained  in  the  animal  kingdom  up  to  this 
level  of  structure. 


THE  MOLLUSKS. 


169 


When  we  come  to  the  single-shelled  mollusks,  such  as 
snails  and  their  kindred,  we  have  the  power  of  motion 
more  constant  than  in  the  bivalve-shelled  mollusks. 
Nearly  all  of  them  can  crawl.  Besides  these,  we  now 


Fig.  74.    Common  Clam,  with  siphon  protruded. 

have  something  like  a  head  to  the  animal.  There  are 
structures  that  do  the  work  of  eyes,  and  feelers  that  serve 
for  the  sense  of  touch,  and  perhaps  organs  that  convey 
the  sense  of  hearing,  all  gathered  about  the  front  end  of 
the  body. 


Fig.  75.    Sea  Snail. 

This  group  of  snail-like,  single-shelled  gasteropod  mol- 
lusks is  also  interesting  for  the  fact  that  it  gives  us  the 
lowest  animals  that  are  able  to  live  upon  the  land.  All 
the  forms  of  animal  life  below  this  level  are  limited  to  the 


170        A   SKETCH   OF   THE  EARTH'S   ORGANIC   LIFE. 

water.  There  are  several  reasons  why  the  lower  mollusks 
cannot  come  upon  the  land.  Their  bodies  are  all  very 
soft,  and  have  no  skin  to  keep  the  water  from  evapor- 
ating in  the  air.  Then,  except  some  of  the  bivalve  shells, 
they  have  no  organs  for  creeping.  When  they  move  at 
all,  they  only  float  in  the  water,  helping  themselves  a  little, 
as  the  jelly-fish  does,  by  flapping  the  projections  of  the 
body. 

The  snails  and  slugs  can  live  and  move  on  the  land  be- 
cause they  have  a  closer  skin,  that  keeps  them  from  drying 
up  so  fast,  and  a  foot  for  crawling ;  and  they  are  fitted  for 
breathing  air  by  having  air-sacks  in  place  of  gills. 


Fig.  76.    Land  Snails. 

The  next  important  group  of  mollusks  contains  our 
squids  or  cuttlefishes,  the  pearly  nautilus,  and  the  paper 
nautilus,  as  well  as  the  strange  form  of  the  ammonites 
and  other  chambered  shells  that  no  longer  exist.  In 
these  creatures,  we  have,  among  the  lowest  forms,  the 
nautilus,  an  animal  that  lives  in  the  outer  room  of  a 
chambered  shell ;  this  shell  constantly  grows  longer  and 
wider,  and  the  animal  moves  forward  in  it,  closing  off  the 
chambered  part  of  the  tube  by  a  partition. 

Around  the  head  are  a  number  of  soft,  fleshy  arms,  that 
enable  the  creature  to  move  over  the  bottom  in  a  slow 


THE  MOLLTJSKS.  171 

and  clumsy  way.  After  a  great  many  changes,  the  cepha- 
lopods,  as  this  group  is  called,  succeed  in  making  a  better 
arrangement  of  their  parts.  The  shell,  which  serves  in 
the  lower  forms  for  moving  the  body,  is  straightened 
out,  made  more  slender,  and  the  body  wrapped  around 
it,  so  that  it  becomes  entirely  enclosed  in  the  animal.  In 
this  position,  it  serves  as  a  skeleton,  enabling  the  animal 
to  have  strong  muscles  to  move  its  limbs.  These  limbs 
are  constructed,  with  a  few  changes,  out  of  the  soft  feelers 
or  suckers  which,  in  the  lower  forms  of  cephalopods,  the 
pearly  nautilus  and  its  kindred,  form  two  rings  around  the 
mouth,  having  a  hundred  or  more  of  the  feelers  in  them. 


Fig.  77.    Section  of  Pearly  Nautilus. 

These  feelers  become  reduced  to  eight  or  ten  in  number. 
They  grow  much  stouter  than  they  were  on  their  inner 
face.  Suckers  and  hooks  for  grappling  are  developed. 
The  mouth  is  provided  with  a  strong  beak.  The  head,  the 
first  complete  head  separated  from  the  body  by  a  neck,  is 
formed ;  strong  fins  are  attached  to  the  sides.  Unlike  the 
lower  mollusks,  this  group  are  strong,  swift  swimmers; 
though  they  sometimes  move  over  the  bottom  by  crawling, 
they  are  so  successful  in  moving  through  the  water  that 
they  seldom  need  this  method  of  motion.  These  squids 
are,  of  all  creatures,  the  quickest  movers  in  the  water, 


172        A   SKETCH   OF   THE   EARTH'S    ORGANIC    LIFE. 

unless  they  are    surpassed   by   some    of  the   most  rapid 
fishes. 

They  move  in  three  different  ways.  By  closing  the  arms 
like  an  umbrella,  they  can  dart  backwards  with  great 
speed.  In  this  motion  they  are  helped  by  the  water, 
which  they  can  squirt  out  of  the  cavity  where  the  gills 
lie.  This  water  passes  through  what  is  called  the  syphon. 
Along  with  this  water,  they  can  throw  out  a  quantity  of 
inky  fluid,  that  darkens  the  water  like  a  cloud,  so  that  the 
creatures  can  quickly  slip  away  unseen  beyond  the  ink- 
clouded  water.  There  is  an  additional  paddling  appara- 
tus in  the  strong  fins  that  are  found  on  the  back  end  of 


Fig.  78.    Cuttle  Fish. 

the  animal.  This  gives  the  squids  the  most  perfect  mech- 
anism for  motion  in  the  world.  They  can  move  forward 
or  backward  with  ease,  and  have  the  peculiar  advantage 
given  by  the  bag  of  sepia,  that  their  flight  is  hidden.  Their 
power  of  grasping  is  also  greater  than  that  of  any  other 
animal.  They  sometimes  grow  to  a  very  large  size.  The 
grasping  arms  are  as  much  as  thirty  feet  long,  and  the 
body  as  large  as  a  flour-barrel.  They  have  been  known 
to  enfold  a  fishing-boat  in  their  arms,  and  only  to  loose 
their  hold  when  one  of  them  was  cut  in  two  with  an  axe. 
The  nervous  system  of  these  squids  is  highly  organized; 


THE  MOLLUSKS.  173 

they  have  such  a  great  amount  of  nervous  tissue  in  the 
part  we  term  a  head,  that  they  may  be  said  to  be  the  first 
animals  to  have  a  distinct  brain.  Without  this  perfect 
nervous  system  they  could  not  possibly  be  as  active  and 
powerful  as  they  are. 

The  mollusks  were  on  earth  in  the  very  earliest  time 
of  which  we  have  any  certain  record  of  life ;  and  in  this 
early  day  we  had  bivalve  shells,  shells  like  our  sea-snails, 
and  the  lowest  cephalopods,  the  orthoceratites ;  but  these 
early  forms  were  inferior  to  those  of  to-day,  so  that  we 
may  fairly  say  that  the  molluscan  life  of  the  earth  has 
grown  to  its  perfection,  through  the  geological  ages;  though 


Fig.  79.    Ancient  Mollusks. 

all  its  most  important  forms  had  been  developed  at  a  very 
early  time. 

Before  leaving  this  very  interesting  group,  we  may 
notice  some  important  features  in  which  they  have  gained 
on  the  lower  animals.  They  are  distinctly  better  than  the 
radiates,  in  that  they  have  more  perfect  powers  of  motion 
and  of  sensation,  and  do  not  need  the  protection  that  is 
gained  in  communities,  such  as  the  corals  generally  form. 
Only  a  few  low  forms  of  mollusks  are  combined  into  com- 
munities, as  are  so  many  of  the  radiates.  In  the  higher 
mollusks,  the  instruments  the  animal's  will  controls  are  far 


174        A   SKETCH    OF   THE   EARTH'S    ORGANIC    LIFE. 

more  perfect  than  in  the  radiates ;  these  mollusks  generally 
take  care  of  their  eggs,  choosing  distinct  places  in  which  to 
deposit  them,  and  not  turning  them  out  into  the  water  with 
no  care,  as  all  the  radiates  do.  This  is  the  lowest  form 
of  that  care  of  the  mother  for  the  young  which  is  such  a 
wonderful  feature  in  the  higher  land  animals. 

The  higher  mollusks  have  very  well  organized  eyes,  and 
large,  separate  breathing  organs ;  their  digestive  system  is 
more  effective,  and  through  it  they  can  digest  more  rapidly 
and  perfectly,  and  so  appropriate  a  larger  store  of  force 
than  the  radiates  can.  Their  circulatory  or  blood  system 
is  now  strong,  and  capable  of  pushing  that  life  and  strength- 
giving  fluid  with  greater  speed  through  the  body. 


THE  ABTICULATES. 


175 


LESSON  IV. 

THE    ARTICULATES. 

NEXT  higher  than  the  mollusks,  in  their  plan  of  struc- 
ture, come  the  creatures  known  as  articulates  or  jointed 
animals.  These  include  all  our  worms,  crabs,  lobsters, 
spiders,  and  insects.  In  fact,  every  creature  which  has  a 
body  made  up  of  rings,  placed  one  after  the  other,  as  in 
the  diagram,  is  an  articulate. 


Fig.  80.    Worms. 

These  successive  rings  are  each  very  much  like  the 
other.  This  likeness  is  sometimes  so  great  that  in  certain 
worms,  if  we  cut  them  in  two,  the  front  part  will  heal, 
and  the  hind  part  form  a  new  head,  and  move  on  without 
risk  of  death.  Some  worms  ordinarily  increase  in  this 
way.  We  cannot  conceive  this  in  any  mollusk,  for  there 
are.  no  such  similar  parts,  or  sets  of  parts,  one  behind  the 
other.  The  only  repetition  of  parts  in  mollusks  is  on 
either  side  of  the  middle  line.  In  the  articulates,  at  least 
among  their  lower  forms,  the  worms,  there  may  be  hun- 
dreds of  these  rings,  each  formed  on  the  same  pattern, 
placed  one  behind  the  other. 


176         A   SKETCH    OF   THE   EARTH'S    ORGANIC   LIFE. 

When  we  come  to  the  crustaceans,  or  such  creatures  as 
the  shrimps,  lobsters,  cray-fish,  and  crabs,  which  are  higher 
than  the  worms,  these  rings  are  fewer  in  number,  and 
more  different  one  from  another.  In  place  of  the  joint- 
less,  spur-like  legs  of  the  worms,  we  have  legs  like  those  of 
a  crab,  lobster,  or  insect,  with  distinct  joints,  which  allow 
a  great  deal  of  motion.  All  these  parts  are  covered  with 
a  hard,  shell-like  skin,  called  ch&tine,  which  protects  them 
from  assailants,  and  at  the  same  time  answers  the  purpose 
of  a  skeleton  to  support  the  muscles  in  their  work.  This 
outer  skeleton  can  be  moulded  into  a  great  variety  of 


Fiy.  81.    Lobster  and  Crabs. 

shapes,  to  suit  the  needs  of  the  animal  it  encases.  In  this 
way,  we  have  a  greater  variety  of  shape  among  the  articu- 
lates than  in  all  the  other  great  groups  of  animals.  This 
ringed  covering  easily  fits  itself  to  changes  of  habits,  so 
that  among  the  articulates  the  will  of  the  animal  finds 
admirable  tools  for  its  use,  in  a  more  perfect  way  than 
among  any  of  the  lower  creatures. 

Among  the  insects,  we  have  a  most  wonderful  variety 
of  structure  and  habits.  They  give  us  such  strangely 
varied  forms  as  the  earwigs,  th^  spiders,  grasshoppers, 
flies,  beetles,  bugs,  and  butterflies.  Indeed,  the  variety  is 
so  great  that  there  are  more  species  or  distinct  kinds 


THE   ARTICULATES.  177 

among  insects  than  among  all  the  other  animals  put  to- 
gether. And  their  habits  or  instincts  are  more  diversified 
than  among  other  animals.  We  now,  for  the  first  time  in 
the  ascending  scale  of  life,  have  a  most  careful  nurture  of 
the  young  by  the  parents, — a  care  that  extends  to  the  most 
elaborate  contrivances  for  keeping  them  from  danger,  and 
providing  them  with  food.  For  the  first  time,  we  find 
communities  of  insects  like  the  ants  and  bees,  which  asso- 
ciate their  labor  for  the  common  profit  of  the  family  or 
colony.  They  not  only  organize  societies,  but  defend 
themselves  with  armies,  and  make  warlike  expeditions  for 
the  supply  and  profit  of  their  communities.  In  many  cases 
the  young  are  fed  on  carefully-chosen  food  prepared  with 
great  labor.  They  build  more  carefully-arranged  habita- 
tions than  any  other  animals,  their  highly-developed  feet 
and  jaws  serving  them  well  in  this  work.  Indeed,  it  is 
first  among  insects,  as  we  follow  up  the  system  of  life,  that 
we  have  any  great  development  of  the  animal  mind. 

The  insects  and  articulates  in  general  are  in  many  ways 
among  the  most  perfect  of  animals.  This  is  true  of  what  we 
call  their  minds  as  well  as  their  bodies.  In  some  strange 
way  they  do,  without  teaching,  things  that  no  other  animal 
save  man  can  be  taught  to  do.  Their  only  physical  defect, 
that  we  can  notice,  is  their  small  size.  A  very  few  of  the 
crustaceans  are  fairly  large  creatures,  but  none  of  the  in- 
sects are  over  an  ounce  in  weight,  and  the  most  of  them  do 
not  weigh  more  than  a  few  grains.  If  they  were  as  large  as 
our  quadrupeds,  or  even  our  birds,  and  were  proportionatel}1" 
as  strong  as  a  wasp  is,  there  would  be  no  place  left  in  the 
world  for  any  other  creatures.  As  it  is,  their  small  size, 
despite  their  means  of  defence,  makes  them  feeble  enemies 
to  most  large  animals.  Yet  the  greatest  difficulties  man 
finds,  in  his  efforts  to  rule  the  earth,  come  from  the  insects. 


178         A   SKETCH    OF   THE   EARTH'S    ORGANIC    LIFE. 

He  can  easily  dispose  of  lions  or  tigers,  but  the  locusts,  the 
white  ants,  and  some  other  insects  dispute  the  empire  with 
him  in  many  regions.  Besides  this,  a  host  of  diseases  of 
his  own  body,  and  those  of  his  domesticated  animals,  come 
from  them. 

The  articulates  are  slowly  developed  in  the  history  of 
the  earth.  They  begin  with  the  worms  and  certain  low 
crustaceans  called  the  trilobites ;  these  two  forms  are  found 
about  as  early  as  we  have  any  distinct  animals.  At  a  later 
date  come  the  crustaceans,  like  our  lobsters  and  crabs ;  but 
not  until  just  before  the  time  of  the  coal  period  do  we 
have  the  insects;  at  the  present  day,  these  insects  are  in 
their  prime,  while  the  worms  are  less  important  than  of 
old,  and  the  crustaceans  have  gained  little  in  the  later 
geological  ages. 


VERTEBRATES.  179 

LESSON  V. 

VERTEBRATES. 

THE  lower  forms  of  life, — the  protozoa,  radiates,  mol- 
lusks,  and  articulates, —  seem  to  have  developed  the  most 
of  their  peculiarities  of  structure  in  the  earlier  stages  of  the 
earth's  history ;  in  the  later  times,  the  backboned  or  verte- 
brate animals,  the  kindred  of  man,  are  the  only  animals 
that  show  us  many  new  plans  of  structures,  or  make  great 
advances  in  the  work  of  building  a  body  for  the  uses  of 
intelligence. 

The  highest  of  the  great  groups  of  animals  is  the  type  of 
vertebrates  or  backboned  ani- 
mals. In  this  group  we  have 
a  plan  of  structure  which  is 
very  different  from  that  of 
the  lower  plans  of  radiates, 
mollusks,  or  articulates.  It 
includes  the  fishes,  reptiles, 
birds,  and  mammals. 

The  principal  forms  of  ver- 
tebrate animals  are  tolerably  Fif>- 82-  AmPhibian- 
familiar  to  all,  so  we  may  give  an  even  briefer  account  of 
them  than  of  the  lower  animals. 

Lowest  in  the  scale  of  vertebrate  life  come  the  fishes. 
In  them  we  find  the  vertebrate  body  shaped  only  for 
swimming :  the  parts  which  are  feet,  or  wings,  or  hands,  in 
their  land  kindred  are,  when  present,  always  in  the  form 
of  fins.  There  is  no  distinct  neck.  Tho  animal  generally 
breathes  by  means  of  gills  placed  in  the  back  part  of  the 
head,  in  the  mouth  cavitv,  which  take  the  air  from  the 


180        A   SKETCH   OF   THE   EARTH'S    ORGANIC   LIFE. 

water.     They  almost  always  lay  eggs,  but  a  few  have  their 
young  born  alive.     Their  blood  is  cold. 

Above  the  fishes  in  structure,  and  closely  related  to 
them,  we  find  the  group  of  vertebrates  known  as  amphi- 
bians, a  name  given  to  them  because  they  generally  live  for 


84.    Salamanders. 


a  part  or  the  whole  of  their  lives  in  the  water,  in  the  form 
of  tadpoles  such  as  those  of  our  common  frog.  In  this 
group  come  the  water-dogs,  the  salamanders,  and  all  our 
frogs  and  toads,  as  well  as  many  strange-shaped  ancient 
forms  that  have  disappeared  from  the  earth.  These  crea- 
tures are  fish-like  for  some  time  after  they  leave  the  egg, 
swimming  with  the  long  tail-fin,  and  breathing  with  gills. 
Some  of  them  never  leave  this  condition,  but  others,  as 
our  frogs,  toads,  and  salamanders,  pass  through  a  wonder- 
ful change,  —  their  tails  shrink,  their  legs  sprout  out  in  their 


VERTEBRATES.  181 

proper  places,  and  their  gills  drop  away,  so  that  they  after- 
wards breathe  the  air,  and  can  live  on  the  land. 

Next  higher  than  the  amphibians  come  the  reptiles, 
which  include  our  lizards,  crocodiles,  alligators,  turtles, 
and  snakes,  as  well  as  a  host  of  great  creatures  belonging 
in  the  ancient  times  of  the  earth,  but  long  since  extinct. 
In  these  creatures  there  is  no  fish-like  tadpole  state ;  they 
all  breathe  by  means  of  lungs  from  the  time  they  leave 
the  egg. 


Fig.  85.    Lizard  and  Flying  Reptile. 

These  are  the  first  very  successful  land  animals :  among 
them  we  find  flying,  swimming,  and  walking  forms;  so, 
for  the  first  time,  those  forms  of  progression  which  gave 
the  vertebrates  their  great  place  in  the  world  were  brought 
into  use.  During  the  middle  ages  of  the  earth's  history, 
and  until  the  suck-giving  creatures  came,  these  reptiles 
were  the  monarchs  of  the  world. 

While  the  reptiles  were  in  their  prime,  the  birds,  the 
next  higher  group  of  animals,  appeared.  At  first  they 
were  a  good  deal  like  feathered  flying  lizards.  Their 
tails  were  long,  like  lizards,  and  theii  jaws  had  sharp,  liz- 
ard-like teeth.  The  great  difference  between  them  and 
reptiles  is  in  the  possession  of  a  covering  of  feathers,  and 
their  very  warm  blood.  It  is  the  warm  coating  of  feathers 


182        A  SKETCH  OF  THE  EARTH'S   ORGANIC   LIFE. 

that  protects  their  bodies  from  the  cold,  and  makes  a  warra 
blood  possible.  This  warm-blooded  condition  is  brought 
about  by  a  stronger  and  more  perfect  circulation,  so  ar- 


Fig.  8(5.  Hesperornis  and  Dinornis.  —  Fossil  Birds. 

ranged  that  each  time  the  blood  makes  the  circuit  of  the 
body  it  is  passed  through  the  lungs,  where,  being  exposed 
to  iihe  air,  a  part  of  its  carbon  is  combined  with  oxygen,  or 
burned,  which  gives  out  a  supply  of  heat  to  be  distributed 


through  the  body.  This  supply  of  heat  is  greater  in 
birds  than  in  any  other  animals;  and,  as  the  activity  of 
the  body  depends  on  the  temperature  of  the  blood,  they 
are  very  strong  for  their  weight. 

Highest  of  all  animals  come  the  mammals.     All  these 


VERTEBRATES.  183 

creatures  have  their  young  born  alive,  and  the  mother 
gives  them  milk. 

There  are  two  principal  divisions  of  this  great  class  of 
mammals.  The  lower  and  earlier  to  live  on  earth  is  that 
to  which  the  kangaroos,  opossums,  and  their  kindred  be- 
long. In  these  the  young  are  born  in  a  very  imperfect 
state,  and  are  sheltered  in  a  pocket  of  the  skin  which 
covers  the  teats  of  the  mothers.  In  this  pouch  they  re- 
main for  some  weeks,  until  they  are  strong  enough  to 
move  about,  and  for  some  time  longer  they  return  to  it  for 
the  mother's  milk  and  for  shelter. 


Fig.  88.    Marsupials  —  Kangaroo  and  Myrmecobius. 

The  other  great  division  of  the  mammals  is  without  this 
pouch,  the  young  being  born  in  a  too  perfect  condition  to 
need  its  help.  This  group  includes  all  our  ordinary  four- 
footed  beasts  and  man  himself.  In  the  mammals,  hair  was 
developed  to  serve  the  purpose  of  keeping  in  the  warmth 
furnished  by  the  warm  blood,  which  they  have  in  common 
with  the  birds.  This  hair,  and  the  milk-giving  by  the 
female,  are  features  that  separate  the  mammals  very  sharply 
from  all  other  animals. 

In  the  vertebrates,  we  first  find  an  internal  jointed 
skeleton  which  provides  two  qhambers  for  the  reception  of 


184        A  SKETCH   OF  THE  EARTH'S   ORGANIC   LIFE. 

the  soft  parts  of  the  body ;  one  enclosed  by  the  ribs  for  the 
organs  that  support  the  mere  animal  life  of  the  body,  such 
as  the  stomach,  the  heart,  and  lungs,  etc.  The  other, 
smaller  and  more  completely  enclosed,  is  formed  by  the 
bones  of  the  head  and  the  backbone,  and  encloses  the  most 
important  parts  of  the  nervous  system,  —  the  brain  and 
the  spinal  cord.  These  backbone  parts  of  the  skeleton  are 
so  jointed  together  as  to  be  at  the  same  time  rigid  and 
elastic,  and  give  a  better  protection  to  the  inner  parts 
while  allowing  a  greater  freedom  of  movement  than  any 
other  arrangement  could  do.  To  this  central  skeleton 
there  are  attached  never  more  than  four  limbs.  These, 
like  the  trunk,  have  an  internal  skeleton  that  supports 
them,  and  enables  their  muscles  to  work  them. 


Fig.  89.    Irish  Elk. 

In  the  importance  of  the  nervous  system,  and  in  the 
arrangement  of  the  limbs,  this  group  of  vertebrates  stands 
apart  from  all  other  animals.  In  no  lower  group  is  the 
nervous  system  so  large  or  so  cared  for ;  in  none  are  the 
limbs  so  determined  in  their  forms,  or  so  fitted  for  varied 
work.  We  see  how  suited  they  are  for  their  work,  when 
we  consider  that  by  simple  yet  effective  changes  they  form 
the  fin  of  a  fish,  the  foot  of  the  horse  or  the  lion,  the  wing 


VERTEBRATES.  185 

of  a  bat,  or  the  hand  of  man ; — all  these  varied  parts  have 
come  by  slow  changes  from  one  ancient  form  of  limb. 

The  nervous  system  permits  the  work  of  a  higher  intel- 
ligence than  we  find  in  the  lower  animals.  In  place  of 
habit  or  instinct,  a  blind,  unreasoning  working  of  impulse, 
we  have,  as  we  go  up  on  the  vertebrates,  a  constant  increase 
in  the  likeness  of  the  mind's  working  to  our  own.  We  see 
among  the  fishes  a  certain  care  for  their  young.  This 
carefulness  of  the  offspring  grows  more  and  more  marked, 
until,  in  the  higher  forms,  such  as  the  birds  and  animals 
that  give  suck,  it  takes  the  form  of  parental  love. 

Not  only  through  the  mind,  but  through  the  body,  these 
vertebrates  give  more  help  to  their  young  than  any  other 
group  of  animals.  Among  those  forms  that  lay  eggs, — the 
fishes,  the  reptiles,  and  the  birds,  —  we  find  a  contrivance 
for  helping  the  young  that  reminds  us  of  what  occurs  in  the 
plant  world.  Among  the  higher  plants  the  young  is  helped 
by  a  store  of  concentrated  food  that  makes  the  mass  of 
the  seed.  While  in  the  lowest  forms  there  is  no  'such 
helpful  store.  Thus,  in  the  lower  animals,  the  parent  gives 
the  young  life  without  placing  in  the  eggs  any  store  of  food 
to  sustain  it  in  the  earliest  work  of  existence.  In  the  fishes 
we  find  that  there  is  some  provision  in  the  egg  for  the  sus- 
tenance of  the  young  while  it  is  making  the  first  stages  of 
its  growth,  though  the  amount  is  but  small,  for  the  fishes 
commonly  lay  many  thousands  of  eggs  at  a  time,  so  that 
not  much  can  be  done  for  any  one.  In  the  reptiles  we  find 
the  eggs  greatly  diminished  in  number ;  and  in  each  a  lar- 
ger store  of  food  is  placed,  forming  a  distinct  yolk.  In  the 
birds  the  eggs  attain  their  perfection  ;  they  are  still  fewer 
than  in  the  reptile,  and  are  often  as  much  as  one  tenth  the 
weight  of  the  parent,  so  large  is  the  store  of  nutrition  that 
is  placed  in  them  for  the  help  of  the  young  in  its  growth. 
Besides  this,  the  mother  by  the  nest,  the  warmth  of  her 


186         A   SKETCH   OF   THE   EAETH'S    ORGANIC   LIFE. 

body,  and  the  food  she  brings  them,  does  much  for  her 
young.  In  the  highest  group  of  vertebrates,  the  mammals, 
when  the  young  are  born  alive,  the  mother's  milk  provides  a 
yet  better  method  of  helping  the  young  in  their  growth.  In 
these,  the  highest  groups  of  vertebrates,  the  birds  and  mam- 
mals, the  blood  is  warm  as  it  is  in  none  of  the  lower  forms. 
This  guards  them  against  changes  of  temperature,  and 
makes  them  better  fitted  to  endure  the  struggle  of  life  in 
cold  regions.  Thus,  with  each  step  of  advance,  there  is 
more  help  given  by  each  generation  to  that  which  is  com- 
ing on  to  take  its  place.  While  we  can  trace  the  improve- 
ment of  animals,  as  we  rise  higher  in  the  scale  of  being,  in 
a  great  many  ways,  there  is  no  other  way  in  which  it  is  so 
beautifully  shown  as  in  these  contrivances  of  mind  and 
body  for  helping  the  weakness  of  the  young. 

The  vertebrates  do  riot  seem  to  have  lived  in  the  earliest 
stages  of  the  earth's  life-history.  They  first  appear  some 
time  after  the  other  groups  of  animals  become  known  to  us. 
First,  come  the  fishes ;  then,  at  a  much  later  date,  in  the 
coal-bearing  rocks,  we  have  creatures  related  to  our  water- 
dogs  and  salamanders ;  then,  just  after  coal,  we  have  the 
kindred  of  our  alligators,  which  for  a  long  time  filled  the 
lands  and  seas  with  many  strange  forms  of  reptiles ;  then, 
in  the  Jurassic  time,  as  it  is  called,  that  is,  some  distance 
above  the  coal,  we  have  the  first  mammals.  These  were  lit- 
tle creatures  related  to  our  opossum,  and  called  pouched 
mammals,  because  they  carry  their  young  in  a  pouch  on 
the  belly  for  some  time  after  they  are  born.  These  first 
suck-giving  animals  were  insect-eaters,  as  are  many  of 
their  kindred  at  the  present  day.  It  is  a  long  time  before 
the  mammals  begin  to  have  the  first  place  among  animals; 
for  many  geological  ages  the  reptiles  still  held  the  control 
of  the  lands,  the  seas,  and  the  air  with  their  giant  forms. 
Finally,  however,  these  reptiles  began  to  fade  away,  and 


VERTEBRATES.  187 

the  mammals  to  grow  larger,  more  varied,  and  more  power- 
ful. The  higher  forms  gave  up  the  use  of  the  pouch, 
which  has  been  kept  only  on  a  few  species  of  opossums 
that  live  in  North  and  South  America,  and  a  hundred  or 
so  kinds  that  are  found  in  Australia.  These  pouched 
species  are  fading  away  from  the  earth,  and  are  being  re- 
placed by  the  non-pouched  forms. 

There  are,  very  many  other  features  in  which  the  verte- 
brates show  their  advance  beyond  the  conditions  of  life  in 
the  earlier  types  of  animals ;  of  these  we  may  only  men- 
tion, here  and  there,  a  striking  case. 

All  the  radiates  and  mollusks  are  entirely  voiceless;  so, 
too,  are  all  the  crustaceans;  only  some  of  the  insects 
having  the  power  of  calling  to  others  of  their  kind ;  and 
in  all  cases  this  is  done  by  rubbing  hard  parts  together,  and 
never  by  anything  like  the  voice,  as  we  understand  it.  But 
nearly  all  the  vertebrates  above  the  fishes  have  some  form 
of  call  made  by  driving  the  air  out  of  the  lungs  in  such  a 
way  that  it  vibrates  membranes  stretched  across  its  path. 
This  voice  is  found  in  its  beginning  in  the  fishes,  some 
of  which  force  air  out  of  their  air-bladders,  which  are 
imperfect  lungs,  and  thereby  make  a  call  that  their  mates 
can  hear.  The  frogs  and  toads  have  distinct  voices ;  so  have 
many  of  the  higher  reptiles.  The  birds  all  have  some 
voice,  and  all  the  mammals  have  it.  This  means  of  com- 
munication between  one  animal  and  another  is  a  sign  of 
growing  sympathy  between  kindred  creatures.  Except 
among  the  insects,  there  is  hardly  a  trace  of  this  feeling 
in  the  animals  below  the  vertebrates ;  it  is  peculiarly  the 
mark  of  the  mammals ;  they  feel  for  and  help  each  other. 

Thus,  we  see  that  the  advance  in  the  mind  of  animals 
seems  to  go  with  the  bettering  of  their  bodies.  The  great 
aim  of  all  animals  seems  to  be  to  get  better  and  better 
means  for  the  ever-growing  intelligence  to  use  in  its  work. 


188        A  SKETCH   OF   THE  EARTH'S   ORGANIC   LIFE. 

Last  of  all,  among  the  great  results  of  this  world,  comes 
man  himself.  In  his  structure  we  see  many  relations  to  the 
other  mammals,  and  there  can  be  no  doubt  that  his  body 
has  been  in  some  way  made  from  the  forms  of  the  mam 
mals  below  him  in  structure,  so  that  man,  as  an  animal, 
stands  in  close  relation  to  the  lower  life  of  the  world ;  but 
when  we  come  to  consider  the  mind  of  man,  we  find  some- 
thing very  widely  different  from  the  mind  of  the  lower 
animals.  In  the  lower  animals  we  find  a  trace  of  all  the 
faculties  we  find  in  man,  but  they,  unlike  man,  are  not 
capable  of  indefinite  advance.  They  are  bound  down  to 
a  certain  narrow  round  of  thought  and  action ;  but  in  man 
we  have  a  creature  able  to  go  forward  without  limit;  so 
that  we  may  say  there  is  no  such  relation  between  his 
mind  and  the  minds  of  lower  creatures,  as  there  is  between 
his  body  and  those  of  animals.  Mentally,  he  belongs  to 
another  system  of  creation  from  the  beasts. 

When  we  study  the  forms  of  the  lower  animals,  we  do 
not  find  one  series  of  steps  leading  up  from  the  lower  to 
the  higher  forms,  but  different  groups,  each  with  its  own 
peculiar  plan  of  structure.  There  have  been  many  experi- 
ments in  the  building  of  habitations  for  intelligence.  The 
most  of  these  have  gained  only  a  partial  success,  for  the 
reason  that  the  plan  of  the  structure  did  not  allow  the 
necessary  perfection  of  the  body.  Of  all  these  efforts,  that 
of  the  vertebrates  was  the  most  promising,  for  it  gave  by 
its  skeleton,  by  its  careful  building  of  the  nervous  system, 
by  its  plan  of  limbs,  the  best  chance  to  go  on  to  a  high 
structure.  Out  cf  the  many  trials,  the  great  success  of 
man  was  at  length  reached. 

The  naturalist  cannot  believe  that  man  was  a  mere  acci- 
dent; he  is  rather  the  being  to  which  the  world  in  all  its 
efforts  was  constantly  tending. 


CHAPTER  X. 


THE  NATURE  AND   TEACHING   OF  FOSSILS. 


LESSON  I. 
HOW  FOSSILS  ARE  FORMED. 

TN  the  later  pages  of  this  book  we  shall  often  have  to 
-*-  speak  of  fossils,  or  the  remains  of  animals  and  plants 
that  are  preserved  in  rocks,  so  that  it  is  well  to  get  an  idea 
of  what  they  are,  and  how  they  are  formed. 

A  few  living  things,  such  as  the  jelly  fishes,  the  slugs  or 
shelless  snails,  etc.,  have  soft  bodies  which  at  death  dis- 
solve and  leave  no  solid  parts  behind.  But  most  animals 
and  plants  at  death  leave  in  the  water  or  upon  the  earth 
bodies  that  have  a  certain  solidity ;  woody  matter  in  the 
case  of  plants,  bones  in  the  case  of  higher  backboned 
animals,  hard  skins  as  in  the  insects,  crabs,  lobsters,  etc., 
or  shelly  matter  as  in  the  shells  and  corals.  If  these  hard 
parts  are  left  uncovered  on  the  surface  of  the  soil  or  on  the 
bottom  of  the  sea  for  a  long  time,  they  utterly  decay  and 
fall  to  dust.  Examine  any  old  forest ;  it  has  grown  for, 
it  may  be,  hundreds  of  thousands  of  years;  if  it  were 
not  for  the  rapid  decay  of  the  leaves  and  branches  that 
fall  on  the  earth,  the  waste-heap  would  be  many  times 
deeper  than  the  tallest  trees  are  high  ;  but  there  are  only  a 
few  inches,  or,  at  most,  a  foot  or  two  of  vegetable  mould 
on  the  ground  where  it  stands.  If  all  the  bones  of  all  the 
birds  and  beasts  that  have  died  in  this  wood  had  remained 


190  THE  NATURE  AND  TEACHING  OP  FOSSILS. 

there,  the  soil  would  have  its  surface  covered  with  these 
remains ;  yet  we  may  search  for  days  and  not  find  a  single 
bone  in  a  square  mile  of  forest.  All  such  remains  rot 
away  speedily ;  the  skeleton  of  an  ox  left  on  the  surface  of 
the  ground  is  decayed  in  a  score  of  years  and  falls  to  pow- 
der. So  we  can  say  that  nearly  all  the  bodies  of  animals 
and  plants  that  die  on  the  land  fall  speedily  to  dust.  Yet 
there  are  certain  ways  in  which  their  remains  may  in  rare 
cases  be  preserved.  If  the  trunk  of  a  tree  falls  into  a  wet 
swamp  or  a  pond,  and  sinks  to  the  bottom,  it  will  only 
partly  decay,  turning  black,  but  retaining  its  shape  for 
many  thousand  years.  Thus,  in  New  Jersey  and  else- 
where, they  dig  out  these  buried  trunks  and  use  them  for 
timber.  Sometimes,  as  in  Ireland,  they  are  found  even 
after  the  forests  in  which  they  grew  have  entirely  disap- 
peared from  the  region.  In  such  swamps  we  often  find  the 
bones  of  animals  which  have  been  drowned  there ;  as,  for 
instance,  in  the  swamps  of  Ireland  are  found  the  bones  of 
the  great  elk,  the  largest  horned  creature  of  the  deer 
tribe  that  we  know.  Then,  too,  we  may  find  the  remains 
of  fishes  and  water  shells.  If  it  happens  that  such  a 
swampy  bed  is  buried  under  the  sea,  and  covered  with 
other  strata,  it  may  preserve  to  us  the  remains  of  a  very 
ancient  time;  such,  in  fact,  are  the  coal-beds  that  are 
now  giving  the  wealth  to  the  greatest  nations  of  the  world. 
It  may  sometimes  occur  that  forests  and  swamps,  with 
the  dead  and  living  things  they  contain,  are  buried  under 
a  shower  of  volcanic  ashes,  or  the  dusty  matter  thrown  out 
by  volcanoes,  and  so  preserved  from  decay.  Or,  it  may 
happen  that  in  limestone  countries,  the  remains  of  animals 
are  swept  into  caverns,  and  buried  under  the  floors  of 
stalactite,  and  so  sealed  up  from  the  air ;  or,  in  yet  other 
cases,  the  remains  may  be  buried  ia  the  beds  of  mud  and 
sand  along  the  banks  of  rivers. 


HOW   FOSSILS   ARE  FORMED.  191 

But  all  these  methods  of  burial  on  the  land  are  not  able 
to  save  much  of  the  forms  of  land  life  from  utter  decay. 
This  we  may  see  by  noticing  how  very  seldom  it  is  that 
we  find  any  remains  of  the  creatures  that  lived  in  this 
country  before  it  was  settled  by  the  whites.  I  doubt  if  my 
readers  have  ever  found  the  bones  of  a  deer,  a  bear,  or  a 
panther  anywheie  in  the  fields  or  in  the  openings  made 
for  roads  or  cellars,  though  scores  of  these  animals  have 
died  on  every  acre  of  the  land.  There  is  no  provision  for 
their  burial,  and  so  they  almost  always  decay. 

So  it  is  on  the  land,  but  in  the  sea  it  is  quite  otherwise : 
there  every  animal  that  leaves'  at  death  a  solid  frame  gives 
its  remains  to  the  bottom,  unless  it  goes  into  the  jaws  of 
some  enemy,  as,  in  truth,  it  oftenest  does.  Once  on  the 
sea-floor,  it  finds  a  host  of  animals  glad  to  use  anything  in 
the  way  of  food  that  the  body  may  afford.  Yet  it  happens 
that  very  many  of  the  dead  that  come  to  the  sea-floor  are 
buried  in  the  mud  or  sand  that  is  constantly  gathering 
there,  and  in  this  way  are  secured  from  decay.  We  need 
only  drag  a  dredge  over  the  sea-floor,  at  almost  any  point 
from  near  the  shore  to  a  depth  of  twenty  thousand  feet,  to 
gather  a  lot  of  this  bottom  mud,  in  which  we  find  shells 
and,  other  hard  parts  of  animals  that  have  been  already 
buried  in  the  muddy  deposit.  We  can  easily  see  that  in 
time  they  would  be  sealed  under  a  great  thickness  of  this 
ever-gathering  waste  that  covers  the  sea-floor  in  a  sheet  as 
wide  as  the  oceans. 

We  have  now  seen  most  of  the  ways  in  which  the  dead 
bodies  of  animals  and  plants  may  be  buried  in  the  earth's 
crust;  we  will  next  try  to  show  how  they  are  preserved 
from  further  decay.  It  usually  happens  that  when  the 
bodies  of  animals  or  plants  are  buried  in  the  rocks,  certain 
changes  occur  in  them.  If  the  remains -are  laid  at  a  little 


192  THE   NATURE   AND   TEACHING    OF    FOSSILS. 

depth  beneath  the  surface,  as  in  human  graves,  the  rain 
water  and  air  penetrate  to  them,  and  they  fall  into  com- 
plete decay,  becoming  mere  dust  that  is  seized  on  by  the 
roots  of  plants,  and  lifted  once  again  into  life.  But  when 
these  remains  are  buried  where  neither  the  rain-water  nor 
the  air  can  get  to  them,  they  may  preserve  their  structure 
fora  very  long  time;  for,  when  these  change-producing 
agents  are  kept  away,  the  principal  forces  that  bring  decay 
are  not  free  to  act  upon  the  remains.  They  are  then  in 
much  the  same  condition  as  the  preserved  vegetables  and 
meats  that  are  enclosed  in  well-sealed  cans,  and  there  is  no 
reason  why  they  should  ever  decay,  for  the  air,  that  by  its 
oxygen  rots  them,  is  shut  out.  So  it  comes  about  that  a 
mammoth  buried  in  the  ice  of  Siberia  can  have  even  its 
eyeballs  preserved  for  some  such  time  as  one  hundred 
thousand  years;  or  that  a  grass-like  plant  buried  in  the 
far  more  ancient  coal-beds  should  keep  so  perfectly  that  it 
remains  flexible  to  the  present  day ;  or  the  shells  of  the 
yet  remoter  Silurian  age  should  keep  a  little  of  the  color 
which  they  had  in  their  time  of  life. 

But  it  generally  happens  that  the  bodies  of  these  buried 
creatures  undergo  certain  changes  that  gradually  destroy 
their  original  shape.  They  are  often  somewhat  heated, 
owing  to  their  deep  burial  beneath  the  rocks  that  are  laid 
down  on  them,  and  their  consequent  holding  in  of  the  heat 
that  comes  up  from  the  depths  of  the  earth.  When  this 
occurs,  the  hot  water  that  lies  around  them  often  takes 
away  the  lime  of  their  bodies,  and  deposits  flinty  matter, 
or  makes  other  changes.  Thus,  it  has  happened  in  a  mine 
in  Utah,  that  around  the  leaves  and  stems  of  fossil  plants 
silver  has  been  found  deposited.  If  the  heat  is  greater,  it 
often  occurs  that  the  whole  of  the  fossil  disappears,  leaving 
only  a  stain  on  the  rock,  or  even  no  trace  of  its  having 


HOW   FOSSILS   ARE   FORMED.  193 

been  there.  When  rocks  like  limestones  become  crystal- 
line, all  the  fossils  commonly  disappear,  though  they  may 
have  been  there  in  great  plenty  and  excellent  preservation. 

Thus,  it  comes  about  that  while  the  creatures  that  live  on 
the  land  are  rarely  preserved  to  us,  those  of  the  sea  are 
often  buried  in  the  rocks ;  and  when  the  rocks  in  which 
they  are  buried  are  lifted  above  the  sea,  and  worn  by  the 
frost  or  rain,  the  fossils  appear  in  great  numbers,  sometimes 
so  thick  as  to  cover  the  hillsides  with  the  well-preserved 
relics  of  a  life  that  passed  away  from  the  earth  many  mil- 
lion years  ago. 

It  is  from  these  remains  that  the  geologist  is  able  to 
make  up  the  history  of  life,  and  to  construct  a  picture  that 
represents  the  animals  and  plants  that  lived  from  time  to 
time  in  the  past.  In  this  work  long  practice  has  given 
great  skill ;  so  that,  from  a  few  bones,  or  a  fragment  of  a 
shell,  it  is  possible  for  a  naturalist  to  form  a  tolerably  clear 
idea  of  the  creature  to  which  these  fragments  belonged, 
and  something  of  its  habits  of  living.  Thus,  the  structure 
of  the  teeth  will  show  us  whether  an  animal  was  flesh  or 
grass  eating,  as  is  seen  in  the  case  of  the  dog  and  sheep, 
where  their  teeth  are  precisely  fitted  for  their  different 
sorts  of  food.  Often,  a  single  tooth  of  any  kind  of  an 
animal  that  has  left  us  no  other  part,  or  fragment  of  an 
insect's  wing  that  is  all  which  has  come  down  to  us,  will 
serve  to  prove  to  trained  eyes  and  minds  the  existence 
of  creatures  of  a  certain  mould  at  a  particular  time  in  the 
past.  So,  out  of  the  shreds  of  the  life  that  lived  in  an- 
cient days,  taking  here  and  there  the  fragments  as  they 
happen  to  come  to  us,  we  can  gradually  build  a  tolerable 
museum  that  will  show  us  how  this  life  stood  at  each  time 
in  this  past.  We  know  in  this  way,  with  perfect  certainty, 
that  over  a  vast  duration  of  time  the  life  of  the  earth's 


194  THE   NATURE   AND   TEACHING   OF   FOSSILS. 

surface  has  been  slowly  changing.  Now  and  again  par- 
ticular kinds  of  animals  and  plants  disappear,  and  theii 
places  are  taken  by  others.  In  this  way  the  whole  of  the 
animals  and  plants  of  our  globe  has  been  many  times 
changed,  the  old  kinds  giving  place  to  newer  and  higher 
forms. 


CHAPTER  XI. 


THE   ORIGIN  OF  ORGANIC  LIFE. 


LESSON  I. 
HOW  NEW  SPECIES  ARE  MADE. 

A  MONG  the  questions  which  the  student  of  the  earth 
-£-*-  finds  always  before  him,  in  the  study  of  its  history, 
are  how  animals  and  plants  have  come  to  be ;  how  this  life 
began  ;  how,  from  time  to  time,  these  living  creatures  have 
disappeared,  and  been  replaced  by  other  kinds.  These  are 
all  hard  questions,  and  we  cannot  yet  give  them  full  an- 
swers. Until  modern  times,  students  did  not  know  that 
there  had  been  a  very  long  history  to  life,  in  which  all  the 
kinds  of  beings  had  often  been  changed,  giving  place  to 
other  kinds  ;  therefore,  until  our  own  day,  the  general  opin- 
ion was  that  all  the  kinds  of  animals  and  plants  now  on 
the  earth  had  been  created  from  the  dust  in  the  shape  we 
find  them.  But,  when  in  this  century  it  was  found  that 
before  the  coming  of  each  of  these  living  animals  and  plants 
there  were  other  forms  closely  resembling  them,  yet  of  dif- 
ferent species,  and  that  this  chain  of  beings  stretched  clear 
back  into  the  past,  the  animals  becoming  more  simple  as  we 
went  towards  the  time  when  life  began,  it  was  gradually 
learned  that  these  animals  had  in  some  way  sprung  from 
each  other.  For  we  cannot  well  believe  that  the  Creator 
would  make  such  relationships  between  creatures,  creating 
each  like  that  which  went  before,  yet  with  a  difference. 


196  THE   ORIGIN   OF   ORGANIC   LIFE. 

It  is  far  more  reasonable  to  believe  that  the  living  forms 
have  sprung  from  the  kindred  forms  that  have  passed  away. 
So  strong  is  this  argument,  that  there  is  probably  not  a 
single  person  living  who  has  been  a  careful  student  of  ani- 
mals or  plants  who  doubts  that  the  life  now  on  earth  has 
sprung  from  species  or  kinds  that  have  passed  away.  The 
only  doubt  is  as  to  the  means  by  which  the  change  from 
one  to  the  other  has  been  brought  about.  This  is  the  ques- 
tion to  which  students  of  nature  are  now  giving  the  most 
of  their  attention. 

So  far  but  one  clear  way  has  been  found  in  which  the 
change  can  be  accounted  for,  and  while  it  cannot  explain 
more  than  a  part  of  the  puzzle,  it  is  an  important  help  to 
our  knowledge  of  life.  This  partial  explanation  is  known 
as  the  Darwinian  theory,  taking  its  name  from  the  stu- 
dent who  first  suggested  it.  This  explanation  rests  on  the 
fact  that  each  animal  and  plant  in  the  world  has  many 
more  offspring  than  can  find  a  place  in  the  world.  Some 
fish,  for  example,  lay  as  many  as  a  hundred  thousand  eggs 
each  year,  while,  on  the  average,  only  one  or  two  of  these 
young  live  to  grow  up,  the  others  of  the  brood  falling  a 
prey  to  enemies  of  one  sort  and  another.  The  result  is 
the  same  with  every  animal  and  plant:  they  have  more 
young  than  the  world  can  give  a  place  to,  for  all  the  seas 
and  lands  have  about  as  many  animals  and  plants  as  they 
can  give  a  chance  to  live ;  so  it  comes  about  that  the  world 
of  life  below  man  is  one  great  conflict,  an  unceasing  battle 
for  life,  where  each  creature  struggles  with  its  neighbor 
who  wants  the  same  food  or  place.  Nearly  every  living 
thing  has  two  sorts  of  enemies  in  the  world:  passive 
enemies,  who  occupy  the  place  in  sea,  on  land,  or  in  the 
air  which  the  new-comer  needs  ;  and  active  enemies  in 
the  creatures  that  prey  upon  it,  and  try  to  make  food 


HOW   NEW   SPECIES   AKE   MADE.  197 

of  its  body.  We  see  that  these  creatures  are  constantly 
trying  new  plans  to  make  themselves  better  fitted  to 
win  success  out  of  their  difficulties :  they  become  swifter 
of  foot  or  wing;  they  get  stronger  defensive  weapons; 
they  invent  new  habits  that  will  elude  their  enemies ;  in 
a  thousand  different  ways  they  change  to  meet  their  needs. 
It  is  certain  that  to  these  chances,  which  serve  to  help 
the  creatures  in  the  long  battle  for  life,  we  owe  a  great 
part  of  the  changes  that  are  constantly  arising  in  the 
forms  of  living  things.  The  only  trouble  arises  when 
we  try  to  see  just  how  the  change  is  brought  about.  We 
may,  in  part,  explain  it  in  this  way:  among  all  the 
young  of  any  animal  or  plant,  each  differs  somewhat 
from  any  other.  These  differences  are  generally  slight, 
but  they  may  be  enough  to  give  the  particular  crea- 
ture a  better  chance  to  live ;  it  may  be  stronger  limbs 
for  flight  or  chase,  or  some  difference  in  habits,  or  any 
other  profitable  quality  of  its  body  or  mind.  In  other 
words,  those  that  vary  in  the  direction  of  profit  will  be 
more  likely  to  survive  in  the  struggle  for  existence  than 
those  that  vary  in  other  directions.  Next,  we  must  notice 
the  fact  that  each  living  creature  is  likely  to  give  its 
peculiar  traits  of  body  and  mind  to  its  descendants,  so 
that  they  will  have  a  share  of  the  same  peculiarities  that 
the  parent  had,  and  on  these  creatures,  the  same  principle 
of  survival  of  those  that  are  fittest  for  success  will  again 
act,  making  the  profitable  feature  stronger  than  it  was  be- 
fore. If  longer  legs  or  stronger  wings  saved  the  parent, 
it  is  likely  to  give  those  longer  legs  or  stronger  limbs  to 
its  offspring,  which  will  give  them  an  advantage  over  the 
children  of  those  other  members  of  the  same  species  that 
have  not  this  peculiarity.  Some  of  these  descendants  of 
the  long-legged  or  strong-winged  animal  will  probably 


198  THE  ORIGIN  OF   ORGANIC  LIFE. 

have  these  parts  better  developed  than  the  parent,  and  so 
its  children  will  get  the  advantage  of  its  cousins,  and  thus 
prevail  over  them.  From  generation  to  generation,  the 
wings  become  stronger,  or  the  legs  larger,  until  a  race  is 
made  that  differs  very  far  from  the  creatures  from  which  it 
originally  came:  that  we  call  it  a  different  species.  In  time, 
all  the  individuals  of  the  species  who  have  not  changed  in 
this  way  will  be  destroyed  by  their  enemies,  so  that  the  old 
species  will  disappear,  and  the  new  take  its  place. 

Although  this  is  a  very  probable  explanation,  and  may 
account  for  many  changes  that  take  place  among  animals, 
it  cannot  be  said  that  it  is  proven,  nor  can  we  expect  to 
have  a  chance  to  prove  it  for  a  long  time  to  come.  The 
life  of  any  one  student  is  but  a  day  compared  with  the 
slow-going  changes  of  the  world,  and  we  know  too  little 
of  the  struggles  of  our  lower  kindred  with  their  enemies 
to  be  able  to  see  just  how  the  fight  goes  with  them.  The 
only  place  where  we  can  see  anything  like  this  process  of 
choosing  the  fit  for  life,  and  the  unfit  for  death,  is  in  our 
household  and  barnyard  animals,  and  the  plants  of  our 
tilled  grounds,  —  these  creatures  which  man  has  seized  on 
and  forced  to  help  him  in  his  particular  battle.  These 
domesticated  plants  are  taken  out  of  the  combat  of  the 
world;  man  does  not  allow  the  wolves  to  seize  his  slow- 
footed  sheep,  nor  the  swift-growing  weeds  to  overcome 
the  plants  of  his  gardens  or  his  fields,  but  in  place  of  the 
selection  of  nature,  he  uses  a  selection  of  his  own  for 
his  own  purposes.  When,  for  instance,  he  finds  among 
the  constant  variations  of  his  sheep,  an  animal  with 
more  wool,  or  with  shorter  legs,  that  make  it  unable  to 
jump  fences,  he  breeds  from  this  animal,  and  sends  the 
others  to  the  butcher.  He  seeks  among  the  young  of  his 
chosen  sheep  the  lambs  that  have  the  best  wool,  or  the 


HOW  NEW   SPECIES   ARE   MADE.  199 

shortest  legs,  and  sells  the  others ;  and  so  in  certain  places 
he  has  lengthened  the  wool  and  shortened  the  legs  of 
these  animals  until  they  are  so  unlike  their  ancestors  of 
fifty  years  ago,  that  if  we  found  the  two  races  wild,  we 
should  call  them  different  species. 

What,  in  one  case,  man  does  for  profit,  he  does  in 
another  to  please  his  fancy.  Dogs  and  pigeons,  for  in- 
stance, he  breeds  for  the  amusement  of  having  different 
kinds ;  and  so  our  dogs  have  come  to  be  of  many  distinct 
forms,  and  between  the  little  sky-terrier,  the  burly  mas- 
tiff, and  the  long-legged,  agile  greyhound,  there  is  a 
greater  difference  of  form  than  between  foxes  and  wolves, 
or  sparrows  and  robins,  —  things  which  we  regard  as  very 
different  species  among  wild  animals. 

The  way  in  which  animals  change  in  the  hands  of  man 
must  be  regarded  as  good  evidence  that  they  may  be  mod- 
ified in  the  hands  of  nature  where  the  penalty  of  death  is 
administered  on  all  who  do  not  conform  to  the  rules  of 
life ;  to  all  who  do  not  strive  to  go  onward  in  the  race. 

Although  we  cannot  regard  this  theory  of  changes 
among  animals  and  plants  as  perfectly  proven,  there  can 
be  little  doubt  that  it  accounts  for  many  of  the  changes 
that  take  place.  It  is  also  likely  that  there  is  a  host  of 
changes,  perhaps  the  greater  part  of  them,  with  which 
these  selective  processes  have  little  to  do.  It  is  not  likely 
that  anything  so  wonderfully  complicated  as  the  world 
of  life  can  be  due  to  one  cause.  We  also  easily  see  that 
this  idea,  at  most,  accounts  for  only  a  small  part  of  the 
wonders  of  animated  nature.  The  real  marvel  is,  not  that 
animals  and  plants  vary,  or  that  their  changes  lead  to  the 
making  of  new  species,  but  that  these  changes  have  not 
been  by  haphazard,  but  in  a  way  that  has  led  from  the 
lowest  creatures  to  man.  It  is  the  fact  that  these  changes 


200  THE   ORIGIN   OF   ORGANIC   LIFE. 

lead  to  such  an  end  that  is  the  really  wonderful  thing. 
We  cannot  believe  that  if  they  occurred  at  haphazard, 
any  such  a  world  as  we  have  could  have  been  made. 

It  must  not  be  thought  that  all  the  changes  that  take 
place  in  the  world  of  plants  and  animals  lead  to  a  higher 
and  more  perfect  life.  If  the  animal  adopts  modes  of  life 
that  require  a  more  perfect  body  or  a  more  active  mind, 
we  find  that  it  goes  upwards  in  its  changes ;  if,  on  the 
other  hand,  it  takes  up  with  baser  ways  than  its  ancestors, 
it  may  become  more  and  more  degraded  in  its  body  and 
mind.  The  snakes,  for  instance,  were  once  four-limbed 


Fig.  90.    Snake,  Cheirotes  and  Bipes. 

animals  that  moved  like  the  lizards,  but  through  change 
of  habits  they  came  to  other  and  lower  needs,  so  that  their 
limbs  were  no  longer  useful,  and  shrunk  away.  A  few  of 
the  serpents  have  a  small  pair  of  forelegs  which  are  so 
small  that  they  serve  scarce  any  other  use,  save  to  show 
how  they  have  been  degraded  from  higher  forms.  The 
sperm  whales  come  from  creatures  nearly  like  our  bears, 
that  were  pretty  well  up  in  the  world  ;  but  their  ancestors 
took  first  to  living  partly  in  the  water  and  partly  on  the 
land :  then,  finally,  to  an  altogether  water-life,  so  they  have 
lost  their  hair,  their  hind  limbs  have  shrunk  away,  their 
fore  limbs  become  reduced  to  paddles,  and  the  whole  body 


HOW    NEW    SPECIES    ARE   MADE.  201 

has  taken  on  the  outside  form  of  a  fish ;  so,  since  the  begin- 
ning of  the  tertiary  time,  the  whales  have  been  degraded 
from  a  high  to  a  low  place  among  mammals.  There  are 
many  other  cases  among  animals  where  the  body,  in  part 
or  in  whole,  has  been  lowered  from  a  higher  plane  of  struc- 
ture to  a  lower  by  the  change  of  habits.  Some  of  the  most 
instructive  of  these  examples  we  find  among  cavern  animals. 
In  them,  the  eyes  sometimes  entirely  disappear,  the  creatures 
having  taken  on  a  habit  of  living  where  the  light  can  be  of 
no  use  to  them. 

It  is  a  fact  that  the  higher  the  level  of  any  animal's  life, 
the  more  the  chance,  that  through  some  change  of  habit 
the  creature  may  lose  the  gains  its  ancestors  made  for  him, 
and  fall,  far  more  swiftly  than  it  rose,  to  a  lower  level  of 
existence.  This  is  doubtless  true  of  man,  as  well  as  of  his 
lower  kindred,  and  especially  true  of  his  moral  and  men- 
tal nature.  Any  degradation  of  habits  lowers  the  indi- 
vidual, and  the  degradation  will  be  handed  on  to  his  chil- 
dren. If  we  realize  this  truth,  it  gives  us  a  keener  sense 
of  our  duty  to  our  whole  nature,  —  to  our  bodies  and  our 
souls ;  our  very  life  depends  upon  a  wonderful  guidance  that 
has  led  us  slowly  up  the  long  ladder  of  life  that  stretches 
from  things  inanimate  to  man.  We  stand  upon  a  moun- 
tain-top nearer  to  Heaven  than  all  else,  with  the  privileges 
that  are  denied  to  other  beings ;  yet  the  very  height  bids 
us  to  tread  carefully,  lest  we  fall  into  the  depths  below. 

With  the  coming  of  man,  the  progress  of  life  on  this 
earth  seems  to  have  been,  in  the  main,  completed.  Some 
changes  may  take  place  in  the  lower  life ;  the  insects  and 
other  lower  groups  may  become  more  varied,  and  rise  to 
a  higher  level,  but  man  is  the  highest  of  all  the  backboned 
animals.  The  earlier  days  of  the  earth  seem  to  have  been 
times  for  the  growth  of  bodies,  while  our  own  time  is 


202  THE  ORIGIN   OF   ORGANIC   LIFE. 

peculiarly  an  age  of  mind.  The  future  of  this  wonderful 
world  comes  each  day  more  and  more  into  the  keeping 
of  man.  He  subjugates  its  animals  and  plants  to  his  uses ; 
destroys  them,  or  changes  their  form  and  habits  to  his 
needs ;  already  he  has  destroyed  several  species  of  birds 
and  other  animals,  and,  though  some  insects  now  baffle 
him,  he  will  doubtless,  in  the  coming  ages,  have  the  whole 
world  at  his  feet.  But,  when  he  comes  to  a  sense  of  the 
duties  which  his  power  lays  upon  him,  he  will  surely  be 
merciful  to  this  poor  dumb  life  that  has  fought  with  his 
ancestors  in  the  great  battle  of  the  world,  through  all  its 
ages,  and  has  failed  to  win  the  crown  of  life  that  is  his 
alone. 


PROOF   THAT   THE   EARTH  IS   VERY   OLD.  203 

LESSON  II. 

PROOF  THAT  THE  EARTH  IS  VERY  OLD. 

IT  is  only  slowly,  and  with  much  difficulty,  that  we  have 
learned  how  ancient  a  thing  our  earth  really  is.  Many 
figurative  accounts  of  its  sudden  creation  have  been 
found  in  the  sacred  books  of  various  Eastern  peoples, 
but  these  accounts  cannot  be  taken  as  representing  the 
primal  facts  of  the  earth's  history.  Man  is,  himself,  so 
short  lived,  that  he  cannot  imagine  the  vast  duration  of 
the  Past  since  life  began  upon  the  earth ;  at  most  he  may 
remember  a  century  of  time,  yet  this  term  of  the  longest 
human  life  falls  like  a  drop  into  the  great  sea  of  geological 
time. 

Let  us  notice  some  of  the  simpler  proofs  of  the  earth's 
great  antiquity.  Take  any  pebble  in  hand:  consider 
what  time  it  requires  to  shape  this  bit  of  stone  to  round- 
ness ;  how  it  must  pound  on  the  seashore,  roll  in  a  river- 
bed, or  grind  beneath  a  glacier  before  it  becomes  slowly 
beaten  into  this  shape ;  yet  there  are  great  masses  of  rocks, 
thousands  of  feet  in  thickness,  and  stretching  for  hundreds 
of  miles,  made  up  of  such  pebbles.  Look  at  the  sands  of 
our  shores,  or  of  the  tens  of  thousands  of  feet  of  sandstones 
that  cover  the  earth,  and  consider  how  long  it  must  have 
required  to  bruise  their  grains  into  this  small  size,  and 
bear  them  into  the  sea  where  they  were  built  into  rocks. 
Then,  after  they  were  built  on  the  sea-floors,  they  have 
been  lifted  into  the  air,  and  afterwards  carved  into  valleys 
and  hills. 

Take  a  thick  section  of  limestones,  say  one  thousand 
feet  in  depth,  such  as  we  may  find  in  many  countries; 


204  THE  ORIGIN  OF   OEGANIC   LIFE. 

consider  that  all  of  it  has  been  in  the  bodies  of  animals 
that  have  grown  and  died  in  the  sea,  slowly  giving  their 
dead  bodies  to  make  the  limey  beds,  it  has  thickened, 
not  faster,  perhaps,  than  the  hundredth  of  an  inch  a  year, 
until  at  the  end  of  one  million  two  hundred  thousand 
years  it  would  be  finished.  There  are  deep  valleys  carved 
in  this  limestone,  such  as  we  may  find  in  many  regions 
where  streams  cut  through  hills  or  mountains.  Now,  in 
old  countries,  such  as  those  of  Europe,  we  can  often  prove 
how  deep  the  valley  has  cut  in  one  thousand  years,  or  in 
the  natural  term  of  life  of  about  twenty  generations  of 
men ;  we  find,  perhaps,  that  the  valley  deepens  at  the  rate 
of  two  feet  in  one  hundred  years ;  but  as  the  valley  is,  say, 
three  thousand  feet  deep,  we  see  that  it  has  required,  at 
least,  two  and  a  half  million  years  for  it  to  be  carved  out. 
In  fact,  there  would  be  a  yet  larger  time  required,  for  the 
reason  that  the  hills  that  form  this  valley  are  slowly  wear- 
ing down,  as  well  as  the  bottom  of  the  valley  itself,  so  that 
if  we  go  back  to  the  time  when  water  began  to  run  down 
these  slopes  and  carve  them  into  hills  and  dales,  we  might 
have  to  go  many  times  as  far  into  the  Past. 

Take  the  Falls  of  Niagara :  these  falls  have  slowly  re- 
treated up  stream  all  the  way  from  Lewistown,  near  Lake 
Ontario,  to  their  present  place  ;  they  are  still  mounting  up 
stream,  as  their  edge  wears  away,  at  the  rate  of  about  foui 
feet  in  one  hundred  years,  so  that  seventy  thousand  years 
has  certainly  elapsed  since  they  began  to  form. 

In  the  peninsula  of  Florida,  the  southern  part  of  it,  at 
least,  has  been  formed  by  successive  coral  reefs,  which 
grow,  one  after  the  other,  further  and  further  southwards. 
Agassiz  has  reckoned  that  it  required  hundreds  of  thous- 
ands of  years  for  these  reefs  to  grow ;  yet  both  these  great 
works,  the  building  of  the  Florida  reefs  and  the  retreat  of 


PROOF   THAT   THE  EARTH   IS   VERY   OLD.  205 

Niagara  Falls  up  to  its  present  point,  are  among  the  most 
recent  things  in  the  shaping  of  the  world,  —  almost  every 
river-valley  and  every  hill  in  America  is  an  older  monu- 
ment of  the  earth's  forces.  We  know  that  the  lands  change 
their  level  very  slowly  along  most  shores ;  the  change  is 
so  slow  that  we  call  the  land  stationary;  the  greatest 
change  is  that  which  is  going  on  in  Sweden,  where  the  land 
rises  as  much  as  three  feet  in  a  hundred  years;  yet  we 
know  that  many  lands  have  been  alternately  sunk  below 
the  seas,  and  lifted  into  the  air,  perhaps  a  score  of  times. 
To  bring  about  such  changes  requires  an  inconceivably 
long  time. 

If  we  study  the  life  history  of  the  earth,  we  find  other 
things  to  show  us  how  long  the  Past  has  been.  Plants 
and  animals  change  but  slowly ;  we  know  that  there 
has  been  very  little  change  in  the  last  four  thousand 
years,  for  in  the  Egyptian  catacombs  we  find  a  host  of 
mummied  animals  and  plants,  every  one  the  same  as  the 
living  kinds.  The  life  on  the  earth  changes  very  slowly, 
one  kind  dying  and  another  coming  in,  so  that  it  requires 
a  vast  period  altogether  to  change  the  life ;  yet  we  know 
that  many  times,  perhaps  fifty  times,  a  nearly  complete 
change  of  life  has  come  about,  so  that  any  creature 
living  through  all  the  ages  that  living  beings  have  been 
on  earth  would  have  been  able  to  see  about  all  the  life 
renewed  by  these  slow  changes,  at  least  fifty  successive 
times  in  the  earth's  history. 

There  are  many  other  evidences  that  the  duration  of 
the  earth's  past  is  far  greater  than  we  can  imagine,  or  in 
any  way  figure  to  ourselves.  Putting  together  all  the  facts 
that  we  have,  it  seems  tolerably  certain  that  since  the  time 
when  the  earth  was  first  fit  for  life,  somewhere  between 
one  hundred  million  and  four  hundred  million  years  have 


206  THE   ORIGIN   OF   ORGANIC   LIFE. 

gone  by.  We  may  build  a  sort  of  picture  of  this  great 
length  of  time  in  this  way :  in  one  mile  there  are  about 
five  thousand  feet ;  call  the  whole  time  of  the  longest  hu- 
man life  one  hundred  years ;  measure  off  one  long  step  on 
this  mile  of  length  to  represent  one  such  human  life,  then 
the  whole  mile  will  represent  only  one-half  a  million  years, 
and  it  would  require,  perhaps,  a  thousand  miles  of  length 
to  give  us  a  diagram  which  should  represent  the  time  since 
life  came  on  the  earth ;  and  three  feet  on  this  length  would 
represent  the  years  of  the  longest-lived  men.  When  we 
have  seen  what  happens  in  the  space  of  one  human  life,  — 
thousands  of  earthquakes  and  volcanic  eruptions ;  thous- 
ands of  great  storms  that  beat  the  shores ;  vast  stretches 
of  land  grown  dry  or  sunk  beneath  the  sea ;  pestilences 
and  famines,  and  a  myriad  other  changes,  and  then  mul- 
tiply these  by  a  thousand  times  a  thousand,  we  gain  some 
faint  idea  of  what  a  epoch  the  world's  past  has  been,  and 
can  imperfectly  imagine  how  great  the  changes  have  been 
in  such  a  time. 

A  large  part  of  the  work  of  the  geologist  consists  in 
an  effort  to  trace  out  the  history  of  this  past,  to  find 
how  the  lands  and  seas  were  shaped  in  the  different  periods 
of  the  earth's  history,  what  creatures  were  living  at  the 
several  times,  and  how  they  were  succeeded  by  other 
and  higher  forms.  This  has  been  slow  and  perplexing 
work,  but  there  have  been  several  thousand  persons  at 
work  upon  it  during  the  past  hundred  years  or  more,  so 
that  we  now  have  a  tolerably  clear  account  of  the  stages 
through  which  the  earth  has  passed  in  its  long  history. 
In  the  following  chapter  a  brief  outline  of  this  wonderful 
history  is  given. 

It  is  not  easy  to  give  in  a  few  words  an  idea  of  how  the 
geologists  have  succeeded  in  patching  out  this  record  of 


PEOOP   THAT   THE   EAETH    IS    VERY    OLD.  207 

the  earth's  long  history,  yet  it  is  important  that  the  reader 
should  get  some  idea  of  the  ways  in  which  it  has  been 
done. 

One  of  the  most  useful  clews  that  we  have  to  the  his- 
tory of  the  earth  is  had  from  the  beds  of  rock  which  we 
may  find  on  the  land.  We  can  show  how  these  beds  teach 
by  noticing  what  is  shown  in  the  figure.  This  represents 
in  a  rough  way  a  section  from  the  Blue  Ridge  of  Virginia, 
westward  to  beyond  Cincinnati,  Ohio.  On  the  right,  the 
crumpled  rocks  are  composed  of  granites  and  other  crystal- 
line rocks ;  to  the  left,  the  beds  show  limestones,  sandstones, 


Fig.  91. 
Section  from  Blue  Ridge  to  west  of  Cincinnati,  Ohio. 

and  slates;  those  covered  with  dots,  conglomerates-, 
those  shaded  black,  the  beds  that  bear  the  coal.  Now,  as 
all  these  beds,  except  the  coal,  were  formed  beneath  the 
sea,  we  perceive  how  great  must  have  been  the  changes 
since  the  earliest  of  them  were  formed.  These  changes  were 
as  follows :  first,  the  mountains  of  the  Blue  Ridge  existed 
as  mountains  rising  above  the  sea  before  all  the  others 
were  formed ;  this  is  shown  by  the  fact  that  the  lowest 
beds  contain  pebbles  worn  from  their  rocks,  and  they  lie 
up  against  the  granites,  etc.,  in  what  is  called  an  unconform- 
able  position ;  that  is,  the  newer  beds  do  not  slope  the 
same  way  as  the  old,  showing  that  the  old  had  been  tilted 


208  THE  ORIGIN   OF   ORGANIC   LIFE. 

and  covered  before  ttie  new  were  formed;  we  see  that 
these  beds  including  the  coal  measures  are  tilted  up  to 
form  the  Alleghenies. 

Going  further  west,  we  see  a  broad  ridge  in  the  rocks. 
At  Cincinnati  there  is  a  very  wide,  low  mountain.  By 
closely  examining  the  position  and  character  of  the  rocks 
here,  we  can  prove  that  this  ridge  was  in  part  formed  long 
before  the  time  of  the  coal.  It  has  on  its  western  side 
fossil  coral  reefs,  such  as  are  now  formed  on  mountains  in 
the  warm  seas  where  a  current  sets  against  their  shores. 
Next,  we  notice  that  the  various  rocks  that  are  repre- 
sented in  this  diagram  are  thickest  towards  the  east, 
and  thin  out  towards  the  west ;  the  beds  of  pebbles 
abound  near  the  Blue  Ridge,  and  fade  out  westwardly  into 
sandstones  or  fine  muds.  This  shows  us  that  the  land 
was  to  the  east  of  the  old  sea-floors  on  which  these  de- 
posits were  laid  down,  for  pebbles  always  grow  smaller  as 
we  go  away  from  the  shores. 

There  are  many  other  ways  in  which  geologists  are  able 
to  infer  the  succession  of  events,  and  the  conditions  that 
existed  on  the  earth's  surface t  in  past  times.  There  are, 
indeed,  many  other  well-founded  conclusions  that  can  be 
drawn  from  this  section  ;  but  enough  has  been  noted  to  in- 
dicate one  of  the  principal  ways  in  which  geologists  work. 
The  rocks  form  a  great  stone  book,  the  pages  are  often 
ragged,  and  the  signs  hard  to  decipher,  but  the  story  is 
still  plain  if  we  study  it  well. 


CHAPTER  XII. 


BRIEF  ACCOUNT    OF    THE  SUCCESSION  OF  EVENTS 
ON  THE  EARTH'S  SURFACE. 


LESSON  I. 
THE  EARTH  BEFORE  ORGANIC  LIFE  BEGAN. 

THE  earliest  stages  of  the  earth's  history  are  not  written 
in  its  rocks,  so  that  all  we  know  about  the  matter 
comes  from  the  studies  of  astronomers  upon  the  distant 
worlds  of  space,  many  of  which  are  passing  through  the 
changes  that  our  world  must  have  endured  in  becoming 
fit  for  life.  These  very  distant  stages  of  change  were 
probably  about  as  described  below. 


92. 


In  the  beginning  our  earth,  along  with  the  sun  and  thb 
other  planets  of  the  solar  system,  existed  as  a  very  large 
mass  of  finely-divided  matter  much  like  a  gas.  Seen  from 


210       EVENTS  ON  THE  EABTH's  SURFACE. 

the  distant  stars  through  a  strong  telescope,  it  would  have 
appeared  as  a  faintly  shining  mass,  like  what  astronomers 
call  nebula.  The  particles  of  this  gas  all  attracted  each 
other,  which  caused  them  to  fall  in  towards  the  centre 
of  the  mass,  and  as  they  fell  they  all  began  to  swing 
around  in  the  same  direction  as  the  planets  now  swing 
around  the  sun.  Then  this  mass  of  matter  began  to  divide 
into  circles  like  those  strange  rings  that  girdle  the  planet 
Saturn.  When  these  rings  became  tolerably  separated 
from  the  mass  within  them,  they  broke  up,  and  were 
gathered  into  a  sphere.  As  the  old  outer  rings  of  Saturn 


Fig.  93.    Rings  of  Saturn. 

have  been  changed  into  moons,  one  after  another  of  these 
rings  formed  in  the  great  mass  of  gas,  and  were  gathered 
into  the  separate  planets.  These  several  planets  each 
then  shrank,  forming  separate  small  rings,  like  the  great 
rings  from  which  they  were  shaped  ;  these  rings  breaking 
to  pieces  produced  the  moons  or  satellites  of  which  all  the 
planets,  except  possibly  Venus  and  Mercury,  have  one  or 
more.  As  if  to  prove  that  this  was  the  way  in  which 
planets  and  moons  were  formed,  the  planet  Saturn  pre- 
serves one  of  its  rings  that  has  not  collapsed  into  a  moon, 
but  remains  as  a  ring,  as  is  shown  in  the  diagram. 
Although  not  perfectly  certain,  it  is  almost  so,  that  this 


THE  EABTH  BEFORE  ORGANIC   LIFE  BEGAN.        211 

is  something  like  the  first  stage  in  the  development  of 
our  earth. 

When  it  first  separated  from  the  great  shrinking  mass 
of  our  solar  system  and  became  a  sphere-like  body,  the 
matter  of  our  world  was  very  likely  still  a  mass  of  gas, 
which  was  more  than  half  a  million  miles  in  diameter, 
extending  beyond  the  orbit  of  the  moon.  It  then  could 
not  have  been  as  solid  as  the  air  that  now  lies  on  its  sur- 
face. But,  as  it  shrank  into  more  and  more  solid  forms, 
it  too  formed  an  outer  ring,  which  in  time  was  broken  up 
and  gathered  into  our  moon. 

As  the  remaining  mass  of  our  earth  became  more  solid 
from  the  falling  of  its  particles  towards  the  centre,  a  great 
deal  of  heat  was  developed.  We  see  when  a  meteor  falls 
on  the  earth,  or  a  hammer  falls  upon  iron,  that  heat  is 
made  to  appear  when  the  motion  is  arrested,  and  as  these 
particles  of  matter  tumbled  towards  the  centre  of  the 
earth's  mass,  the  whole  gradually  became  hotter  and 
hotter,  until  the  gas  was  by  the  crowding  together  of  its 
particles  converted  into  a  very  hot  fluid  sphere,  not  much 
larger  than  the  present  earth.  As  the  vacant  space  out* 
side  of  the  earth  was  exceedingly  cold,  having  a  temper- 
ature of  one  or  two  hundred  degrees  below  zero,  this  great 
boiling  mass  of  earth-matter  slowly  parted  with  its  heat, 
until  it  became  solid  enough  to  bear  a  crust  of  frozen 
rocks  that  enclosed  the  hotter  matter  within.  Then  the 
water  which  had  been  kept  in  the  state  of  gas  above  the 
earth  came  down  upon  its  surface  and  wrapped  it  with 
the  oceans.  Now,  for  the  first  time,  the  earth  began  to 
be  like  the  world  we  know ;  the  machinery  of  its  physi- 
cal life,  the  winds,  the  ocean-currents,  and  the  rivers, 
came  into  being,  and  all  was  made  ready  for  life  to  begin. 
In  what  way  life  began  we  do  not  know ;  we  only  know 


212       EVENTS  ON  THE  EARTH'S  SURFACE. 

that  all  our  experiments  appear  to  show  that  life,  even  in 
the  lowest  forms,  seems  to  be  always  derived  from  other 
life,  and  not  able  to  start  even  in  the  simplest  forms  from 
dead  matter.  But  once  begun,  the  whole  world  of  progress 
became  open  to  it. 


HISTORY  OF  ORGANIC  LITE.  213 

LESSON  II. 

HISTORY  OF  ORGANIC  LIFE. 

THE  geologist  cannot  find  his  way  back,  in  the  record  of 
the  great  stone  book,  to  the  far-off  day  when  life  began. 
The  various  changes  that  come  over  rocks  from  the  action 
of  heat,  of  water,  and  of  pressure,  have  slowly  modified 
these  ancient  beds,  so  that  they  no  longer  preserve  the 
frames  of  the  animals  that  were  buried  in  them. 

These  old  rocks,  which  are  so  changed  that  we  cannot 
any  longer  make  sure  that  any  animals  lived  hi  them,  are 
called  the  "archsean,"  which  is  Greek  for  ancient.  They 
were  probably  mud  and  sand  and  limestone  when  first 
made,  but  they  have  been  changed  to  mica  schists,  gneiss, 
granite,  marble,  and  other  crystalline  rocks.  When  any 
rock  becomes  crystalline,  the  fossils  dissolve  and  disap- 
pear, as  coins  lose  their  stamp  and  form  when  they  are 
melted  in  the  jeweller's  gold-pot. 

These  ancient  rocks  that  lie  deepest  in  the  earth  are 
very  thick,  and  must  have  taken  a  great  time  in  building ; 
great  continents  must  have  been  worn  down  by  rain  and 
waves  in  order  to  supply  the  waste  out  of  which  they 
were  made.  It  is  tolerably  certain  that  they  took  as 
much  time  during  their  making  as  has  been  required  for 
all  the  other  times  since  they  were  formed.  During  the 
vast  ages  of  this  archaean  the  life  of  our  earth  began  to  be. 
We  first  find  many  certain  evidences  of  life  in  the  rocks 
which  lie  on  top  of  the  archaean  rook,  and  are  known 
as  the  Cambrian  and  Silurian  periods.  There  we  have 
creatures  akin  to  our  corals  and  crabs  and  worms, 
and  others  that  are  the  distant  kindred  of  the  cuttle- 


214 


EVENTS  ON  THE  EARTH'S  SURFACE. 


fishes  and  of  our  lamp-shells.  There  were  no  backboned 
animals,  that  is  to  say,  no  land  mammals,  reptiles,  or 
fishes  at  this  stage  of  the  earth's  history.  It  is  not  likely 
that  there  was  any  land  life  except  of  plants  and  those 
forms  like  the  lowest  ferns,  and  probably  mosses.  Nor 
is  it  likely  that  there  were  any  large  continents  as  at  the 
present  time,  but  rather  a  host  of  islands  lying  where  the 
great  lands  now  are,  the  budding  tops  of  the  continents 
just  appearing  above  the  sea. 

Although  the  life  of  this  time  was  far  simpler  than  ai 
the  present  day,  it  had  about  as  great  variety  as  we  would 
find  on  our  present  sea-floors.  There  were  as  many  dif- 
ferent species  living  at  the  same  time  on  a  given  surface. 


Fig.  94.    North  America  in  Cambrian  time. 

The  Cambrian  and  Silurian  time  —  the  time  before  the 
coming  of  the  fishes  —  must  have  endured  for  many  mil- 
lion years  without  any  great  change  in  the  world.  Hosts 
of  species  lived  and  died ;  half  a  dozen  times  or  more  the 
life  of  the  earth  was  greatly  changed.  New  species  came 
much  like  those  that  had  gone  before,  and  only  a  little  gain 
here  and  there  was  perceptible  at  any  time.  Still,  at  the 
end  of  the  Silurian,  the  life  of  the  world  had  climbed  some 
steps  higher  in  structure  and  in  intelligence. 


HISTORY  OF   ORGANIC   LIFE.  215 

The  next  set  of  periods  is  known  as  the  Devonian.  It 
is  marked  by  the  rapid  extension  of  the  fishes;  for,  al- 
though the  fishes  began  in  the  uppermost  Silurian,  they 
first  became  abundant  in  this  time.  These,  the  first  strong- 
jawed  tyrants  of  the  sea,  came  all  at  once,  like  a  rush  of 
the  old  Norman  pirates  into  the  peaceful  seas  of  Gt. 
Britain.  They  made  a  lively  time  among  the  sluggish 
beings  of  that  olden  sea.  Creatures  that  were  able  to 
meet  feebler  enemies  were  swept  away  or  compelled  to 
undergo  great  changes,  and  all  the  life  of  the  oceans 
seems  to  have  a  spur  given  to  it  by  these  quicker-formed 
and  quicker-willed  animals.  In  this  Devonian  section  of 
our  rocks  we  have  proofs  that  the  lands  were  extensively 
covered  with  forests  of  low  fern  trees,  and  we  find  the 
first  trace  of  air-breathing  animals  in  certain  insects  akin 
to  our  dragon-flies.  In  this  stage  of  the  earth's  history 
the  fishes  grew  constantly  more  plentiful,  and  the  seas 
had  a  great  abundance  of  corals  and  crinoids.  Except  for 
the  fishes,  there  were  no  very  great  changes  in  the  char- 
acter of  the  life  from  that  which  existed  in  the  earlier 
time  of  the  Cambrian  and  Silurian.  The  animals  are 
constantly  changing,  but  the  general  nature  of  the  life 
remains  the  same  as  in  the  earlier  time. 

In  the  Carboniferous  or  coal-bearing  age,  we  have  the 
second  great  change  in  the  character  of  the  life  on  the 
earth.  Of  the  earlier  times,  we  have  preserved  only 
the  rocks  formed  in  the  seas.  But  rarely  do  we  find  any 
trace  of  the  land  life  or  even  of  the  life  that  lived  along  the 
shores.  In  this  Carboniferous  time,  however,  we  have  very 
extensive  sheets  of  rocks  which  were  formed  in  swamps  in 
the  way  shown  in  the  earlier  part  of  this  book.  They  con- 
stitute our  coal-beds,  which,  though  much  worn  away  by 
rain  and  sea,  still  cover  a  large  part  of  the  land  surface. 


216       EVENTS  ON  THE  EARTH'S  SURFACE. 

These  beds  of  coal  grew  in  the  air,  and,  although  the  swamps 
where  they  were  formed  had  very  little  animal  life  in  them, 
we  find  some  fossils  which  tell  us  that  the  life  of  the  land 
was  making  great  progress ;  there  are  new  insects,  includ- 
ing beetles,  cockroaches,  spiders,  and  scorpions,  and,  what 
is  far  more  important,  there  are  some  air-breathing,  back- 
boned animals,  akin  to  the  salamanders  and  water-dogs  of 
the  present  day.  These  were  nearly  as  large  as  alligators, 
and  of  much  the  same  shape,  but  they  were  probably 
born  from  the  egg  in  the  shape  of  tadpoles  and  lived  for 
a  time  in  the  water  as  our  young  frogs,  toads,  and  sala- 


Fig,  95.   Raniceps  Lyelli  —  Coal  time  salamander. 

manders  do.  This  is  the  first  step  upwards  from  the 
fishes  to  land  vertebrates ;  and  we  may  well  be  interested 
in  it,  for  it  makes  one  most  important  advance  in  crea- 
tures  through  whose  lives  our  own  existence  became  pos- 
sible. Still,  these  ancient  woods  of  the  coal  period  must 
have  had  little  of  the*  life  we  now  associate  with  the 
forests;  there  were  still  no  birds,  no  serpents,  no  true 
lizards,  no  suck-giving  animals,  no  flowers,  and  no  fruits. 
These  coal-period  forests  were  sombre  wastes  of  shade, 
with  no  sound  save  those  of  the  wind,  the  thunder,  and 
the  volcano,  or  of  the  running  streams  and  the  waves  on 
the  shores. 


HISTORY   OF   ORGANIC   LIFE.  217 

In  the  seas  of  the  Carboniferous  time,  we  notice 
that  the  ancient  life  of  the  earth  is  passing  away.  Many 
creatures,  such  as  the  trilobites,  die  out,  and  many 
other  forms  such  as  the  crinoids  or  sea  lilies  become 
fewer  in  kind  and  of  less  importance.  These  marks  of 
decay  in  the  marine  life  continue  into  the  beds  just  after 
the  Carboniferous,  known  as  the  Permian,  which  are  really 
the  last  stages  of  the  coal-bearing  period. 

When  with  the  changing  time  we  pass  to  the  beds 
known  as  the  Triassic,  which  were  made  just  after  the  close 
of  the  Carboniferous  time,  we  find  the  earth  undergoing 
swift  changes  in  its  life.  The  moist  climate  and  low  lands 
that  caused  the  swamps  to  grow  so  rapidly  have  ceased  to 
be,  and  in  their  place  we  appear  to  have  warm,  dry  air 
and  higher  lands. 


Fig.  96.    Cycas  circinalis,  akin  to  highest  plants  of  coal  time. 

On  these  lands  of  the  Triassic  time  the  air-breathing  life 
made  very  rapid  advances.  The  plants  are  seen  to  un- 
dergo considerable  changes.  The  ferns  no  longer  make 
up  all  the  forests,  but  trees  more  like  the  pines  began  to 
abound,  and  insects  became  more  plentiful  and  more 
varied.  .; 

Hitherto  the  only  land  back-boned  animal  was  akin  to 
uur  salamanders.  Now  we  have  true  lizards  in  abund- 


218 


EVENTS  ON  THE  EARTH'S  SURFACE. 


ance,  many  of  them  of  large  size.  Some  of  them  were 
probably  plant-eaters,  but  most  were  flesh-eaters;  some 
seem  to  have  been  tenants  of  the  early  swamps,  and 
some  dwelt  in  the  forests. 

The  creatures  related  to  the  salamanders  have  increased 
in  the  variety  of  their  forms  to  a  wonderful  extent.  We 
know  them  best  by  the  tracks  which  they  have  left  on 
the  mud  stones  formed  on  the  borders  of  lakes  or  the  edge 
of  the  sea.  In  some  places  these  footprints  are  found  in 
amazing  numbers  and  perfection.  The  best  place  for 
them  is  in  the  Connecticut  Valley,  near  Turner's  Falls, 


N^ 


Fig.  97.   Foot-prints,  Connecticut  Sandstones. 

Mass.  At  this  point  the  red  sandstone  and  shale  beds, 
which  are  composed  of  thin  layers  having  a  total  thickness 
of  several  hundred  feet,  are  often  stamped  over  by  these 
footprints  like  the  mud  of  a  barnyard.  From  the  little 
we  can  determine  from  these  footprints,  the  creatures 
seem  to  have  been  somewhat  related  to  our  frogs,  but 
they  generally  had  tails,  and,  though  provided  with  four 
legs,  were  in  the  habit  of  walking  on  the  hind  ones  alone 
like  the  kangaroo.  A  few  of  these  tracks  are  shown  in  the 
figure  on  this  page. 

These  strange  creatures  were  of  many  different  species. 
Some  of  them  must  have  been  six  or  seven  feet  high, 


HISTORY   OP   ORGANIC   LIFE.  219 

for  their  steps  are  as  much  as  three  feet  apart,  and  seem 
to  imply  a  creature  weighing  several  hundred  pounds. 
Others  were  not  bigger  than  robins.  Strangely  enough,  we 
have  never  found  their  bones 
nor  the  creatures  on  which 
they  fed,  and  but  for  the  for- 
mation of  a  little  patch  of 
rocks  here  and  there  we 
should  not  have  had  even 
these  footprints  to  prove  to 
us  that  such  creatures  had 
lived  in  the  Connecticut  Val- 
ley in  this  far-off  time.  Fig.  98.  Foot-print, Turners  Falls. 

But  these  wonderful  forms  are  less  interesting  than  two 
or  three  little  fossil  jaw-bones  that  prove  to  us  that  in  this 
Triassic  time  the  earth  now  bore  another  animal  more  akin 


Fig.  99. 
Dromotherium  Sylvestre  and  Teeth  of  Microlestes  antiquus. 

to  ourselves,  in  the  shape  of  a  little  creature  that  gave 
suck  to  its  young.  Once  more  life  takes  a  long  upward 
step  in  this  little  opossum-like  animal,  perhaps  the  first 
creature  whose  young  was  born  alive.  These  little  crea- 
tures, called  Microlestes  or  Dromatherium,  of  which  only 
one  or  two  different  but  related  species  have  been  found 
in  England  and  in  North  Carolina,  appear  to  have  been  in- 


220 


EVENTS  ON  THE  EARTH  S  SURFACE. 


sect-eaters  of  about  the  size  and  shape  of  the  Australian 
creature  shown  in  Fig.  100.  So  far  we  know  it  in  but  few 
specimens,  —  altogether  only  an  ounce  or  two  of  bones, — 
but  they  are  very  precious  monuments  of  the  past. 

In  this  Triassic  time  the 
climate  appears  to  have  been 
rather  dry,  for  in  it  we  have 
many  extensive  deposits  of 
salt  formed  by  the  evapora- 
tion of  closed  lakes,  of  seas, 
such  as  are  now  forming  on 
the  bottom  of  the  Dead  Sea, 
and  the  Great  Salt  Lake  of 
Utah,  and  a  hundred  or  more 
other  similar  basins  of  the 
present  day. 

In  the  sea  animals  of  this  time  we  find  many  changes. 
Already  some  of  the  giant  lizard-like  animals,  which  first 
took  shape  on  the  land,  are  becoming  swimming  animals. 


Fig.  101.   Icthyosaurus  and  Plesiosaurus. 

They  change  their  feet  to  paddles,  which,  with  the  help 
of  a  flattened  tail,  force  them  swiftly  through  the  water. 

The   fishes   on   which    these    great    swimming    lizards 
preyed  are  more  like  the  fishes  of  our  present  day  than 


HISTORY  OP  ORGANIC   LIFE.  221 

they  were  before.  The  trilobites  are  gone,  and  of  the  cri- 
noids  only  a  remnant  is  left.  Most  of  the  corals  of  the 
earlier  days  have  disappeared,  but  the  mollusks  have  not 
changed  more  than  they  did  at  several  different  times  in 
the  earlier  stages  of  the  earth's  history. 

After  the  Trias  comes  a  long  succession  of  ages  in 
which  the  life  of  the  world  is  steadily  advancing  to 
higher  and  higher  planes;  but  for  a  long  time  there  is  no 
such  startling  change  as  that  which  came  in  the  passage 
from  the  coal  series  of  rocks  to  the  Trias.  This  long  set 
of  periods  is  known  to  geologists  as  the  age  of  reptiles. 


Fig.  102.  Reptiles  of  Jurassic  Period. 

It  is  well  named,  for  the  kindred  of  the  lizards  then  had 
the  control  of  the  land.  There  were  then  none  of  our 
large  fish  to  dispute  their  control,  so  they  shaped  them- 
selves to  suit  all  the  occupations  that  could  give  them  a 
chance  for  a  living.  Some  remained  beasts  of  prey  like 
our  alligators,  but  grew  to  larger  size ;  some  took  to  eat- 
ing the  plants,  and  came  to  walk  on  their  four  legs  as  our 
ordinary  beasts  do,  no  longer  dragging  themselves  on 
their  bellies  as  do  the  lizard  and  alligator,  their  lower 
kindred.  Others  became  flying  creatures  like  our  bats, 
only  vastly  larger,  often  with  a  spread  of  wing  of  fifteen 
or  twenty  feet.  Yet  others,  even  as  strangely  shaped, 
dwelt  with  the  sharks  in  the  sea. 


222  EVENTS   ON   THE   EARTH'S    SURFACE. 

In  this  time  of  the  earth's  history  we  have  the  first  bird- 
like  forms.  They  were  feathered  creatures,  with  bills  car- 
rying true  teeth,  and  with  strong  wings ;  but  they  were 
reptiles  in  many  features,  having  long,  pointed  tails  such 
as  none  of  our  existing  birds  have.  They  show  us  that 
the  birds  are  the  descendants  of  reptiles,  coming  off  from 
them  as  a  branch  does  from  the  parent  tree.  The  tor- 
toises began  in  this  series  of  rocks.  At  first  they  are 
marine  or  swimming  forms,  the  box-turtles  coming  later. 
Here  too  begin  many  of  the  higher  insects.  Creatures 
like  moths  and  bees  appear,  and  the  forests  are  enlivened 
with  all  the  important  kinds  of  insects,  though  the  species 
were  very  different  from  those  now  living. 

In  the  age  of  reptiles  the  plants  have  made  a  consid- 
erable advance.  Palms  are  plenty  ;  forms  akin  to  our 
pines  and  firs  abound,  and  the  old  flowerless  group  of 
ferns  begins  to  shrink  in  size,  and  no  longer  spreads  its 
feathery  foliage  over  all  the  land  as  before.  Still  there 
were  none  of  our  common  broad-leaved  trees ;  the  world 
had  not  yet  known  the  oaks,  birches,  maples,  or  any  of  our 
hard-wood  trees  that  lose  their  leaves  in  autumn  ;  nor 
were  the  flowering  plants,  those  with  gay  blossoms,  yet 
on  the  earth.  The  woods  and  fields  were  doubtless  fresh 
and  green,  but  they  wanted  the  grace  of  blossoms,  plants, 
and  singing-birds.  None  of  the  animals  could  have  had 
the  social  qualities  or  the  finer  instincts  that  are  so  com- 
mon among  animals  of  the  present  day.  There  were  prob- 
ably no  social  animals  like  our  ants  and  bees,  no  merry 
singing  creatures;  probably  no  forms  that  went  in  herds. 
Life  was  a  dull  round  of  uncared-for  birth,  cruel  self- 
seeking,  and  of  death.  The  animals  at  best  were  clumsy, 
poorly-endowed  creatures,  with  hardly  more  intelligence 
than  our  alligators. 


HISTORY   OF   ORGANIC   LIFE.  223 

The  little  thread  of  higher  life  begun  in  the  Micro- 
lestes  and  Dromatherium,  the  little  insect-eating  mammals 
of  the  forest,  is  visible  all  through  this  time.  It  held  in 
its  warm  blood  the  powers  of  the  time  to  come,  but  it 
was  an  insignificant  thing  among  the  mighty  cold-blooded 
reptiles  of  these  ancient  lands.  There  are  several  species 
of  them,  but  they  are  all  small,  and  have  no  chance  to 
make  headway  against  the  older  masters  of  the  earth. 

The  Jurassic  or  first  part  of  the  reptilian  time  shades 
insensibly  into  the  second  part,  called  the  Cretaceous, 
which  immediately  follows  it.  During  this  period  the 
lands  were  undergoing  perpetual  changes;  rather  deep 
seas  came  to  cover  much  of  the  land  surfaces,  and  there 
is  some  reason  to  believe  that  the  climate  of  the  earth 
became  much  colder  than  it  had  been,  at  least  in  those 
regions  where  the  great  reptiles  had  flourished.  It  may  be 
that  it  is  due  to  a  colder  climate  that  we  owe  the  rapid 
passing  away  of  this  gigantic  reptilian  life  of  the  previous 
age.  The  reptiles,  being  cold-blooded,  cannot  stand  even 
a  moderate  winter  cold,  save  when  they  are  so  small  that 
they  can  crawl  deep  into  crevices  in  the  rocks  to  sleep  the 
winter  away,  guarded  from  the  cold  by  the  warmth  of  the 
earth.  At  any  rate  these  gigantic  animals  rapidly  ceased 
to  be,  so  that  by  the  middle  of  the  cretaceous  period  they 
were  almost  all  gone,  except  those  that  inhabited  the  sea ; 
and  at  the  end  of  this  time  they  had  shrunk  to  lizards  in 
size.  The  birds  continue  to  increase  and  to  become  more 
like  those  of  our  day ;  their  tails  shrink  away,  their  long 
bills  lose  their  teeth ;  they  are  mostly  water-birds  of  large 
size,  and  there  are  none  of  our  songsters  yet;  still  they 
are  for  the  first  time  perfect  birds,  and  no  longer  half- 
lizard  in  their  nature. 

The  greatest  change  in  the  plants  is  found  in  the  conv 


224        EVENTS  ON  THE  EARTH'S  SURFACE. 

ing  of  the  broad-leaved  trees  belonging  to  the  families  of 
our  oaks,  maples,  etc.  Now  for  the  first  time  our  woods 
take  on  their  aspect  of  to-day;  pines  and  other  cone- 
bearers  mingle  with  the  more  varied  foliage  of  nut-bearing 
or  large-seeded  trees.  Curiously  enough,  we  lose  sight  of 
the  little  mammals  of  the  earlier  time.  This  is  probably 
because  there  is  very  little  in  the  way  of  land  animals  of 
this  period  preserved  to  us.  There  are  hardly  any  mines 
or  quarries  in  the  beds  of  this  age  to  bring  these  fossils 
to  light.  In  the  most  of  the  other  rocks  there  is  more  to 
tempt  man  to  explore  them  for  coal  ores  or  building 
stones. 

In  passing  from  the  Cretaceous  to  the  Tertiary,  we  enter 
upon  the  threshold  of  our  modern  world.  We  leave  be- 
hind all  the  great  wonders  of  the  old  world,  the  gigantic 
reptiles,  the  forests  of  tree  ferns,  the  seas  full  of  ammo- 
nites and  belemnites,  and  come  among  the  no  less  wonder- 
ful but  more  familiar  modern  forms.  We  come  at  once 
into  lands  and  seas  where  the  back-boned  animals  are  the 
ruling  beings.  The  reptiles  have  shrunk  to  a  few  low 
forms,  —  the  small  lizards,  the  crocodiles  and  alligators, 
the  tortoises  and  turtles,  and,  as  if  to  mark  more  clearly 
the  banishment  of  this  group  from  their  old  empire,  the 
serpents,  which  are  peculiarly  degraded  forms  of  reptiles 
which  have  lost  the  legs  they  once  had,  came  to  be  the 
commonest  reptiles  of  the  earth. 

The  first  mammals  that  have  no  pouches  now  appear. 
In  earlier  times,  the  suck-giving  animals  all  belonged  to 
the  group  that  contains  our  opossums,  kangaroos,  etc. 
These  creatures  are  much  lower  and  feebler  than  the 
mammals  that  have  no  pouches.  Although  they  have 
probably  been  on  the  earth  two  or  three  times  as  long  as 
the  higher  mammals,  they  have  never  attained  any  emi- 


HISTORY  OF   ORGANIC   LIFE.  225 

nent  success  whatever  ;  they  cannot  endure  cold  climates  ; 
none  of  them  are  fitted  for  swimming  as  are  the  seals  and 
whales,  or  for  flying  as  the  bats,  or  for  burrowing  as  the 
moles ;  they  are  dull,  weak  things,  which  are  not  able  to 
contend  with  their  stronger,  better-organized,  higher  kin- 
dred. They  seem  not  only  weak,  but  unable  to  fit  them- 
selves to  many  different  kinds  of  existence. 

In  the  lower  part  of  the  Tertiary  rocks,  we  find  at  once 
a  great  variety  of  large  beasts  that  gave  suck  to  tkeir 
young.  It  is  likely  that  these  creatures  had  come  into 
existence  in  a  somewhat  earlier  time  in  other  lands, 
where  we  have  not  been  able  to  study  the  fossils ;  for  to 
make  their  wonderful  forms  slowly,  as  we  believe  them  to 
have  been  made,  would  require  a  very  long  time.  It  is 
probable  that  during  the  Cretaceous  time,  in  some  land 
where  we  have  not  yet  had  a  chance  to  study  the  rocks, 
these  creatures  grew  to  their  varied  forms,  and  that  in  the 
beginning  of  the  tertiary  time,  they  spread  into  the  re- 
gions where  we  find  their  bones. 

Beginning  with  the  Tertiary  time,  we  find  these  lower 
kinsmen  of  man,  through  whom  man  came  to  be.  The 
mammals  were  marked  by  much  greater  simplicity  and 
likeness  to  each  other  than  they  now  have.  There  were 
probably  no  monkeys,  no  horses,  no  bulls,  no  sheep,  no 
goats,  no  seals,  no  whales,  and  no  bats.  All  these  animals 
had  many-fingered  feet.  There  were  no  cloven  feet  like 
those  of  our  bulls,  and  no  solid  feet  as  our  horses  have. 
Their  brains,  which  by  their  size  give  us  a  general  idea  of 
the  intelligence  of  the  creature,  are  small ;  hence  we  con- 
clude that  these  early  mammals  were  less  intelligent  than 
those  of  our  day. 

It  would  require  volumes  to  trace  the  history  of  the 
growth  of  these  early  mammals,  and  show  how  they,  step 


226  EVENTS  ON  THE  EARTH'S  SURFACE. 

by  step,  came  to  their  present  higher  state.  We  will  take 
only  one  of  the  simplest  of  these  changes,  which  happens 
to  be  also  the  one  which  we  know  best.  This  is  the 
change  that  led  to  the  making  of  our  common  horses, 
which  seem  to  have  been  brought  into  life  on  the  conti- 
nent of  North  America.  The  most  singular  thing  about 
our  horses  is  that  the  feet  have  but  one  large  toe  or 
finger,  the  hoof,  the  hard  covering  of  which  is  the  nail  of 
that  extremity.  Now  it  seems  hard  to  turn  the  weak, 
five-fingered  feet  of  the  animals  of  the  lower  tertiary — feet 
which  seem  to  be  better  fitted  for  tree-climbing  than  any- 
thing else  —  into  feet  such  as  we  find  in  the  horse.  Yet 


Fig.  103.   Feet  of  Tertiary  Mammals. 

the  change  is  brought  about  by  easy  stages  that  lead  the 
successive  creatures  from  the  weak  and  loose-jointed  foot 
of  the  'ancient  forms  to  the  solid,  single-fingered  horse's 
hoof,  which  is  wonderfully  well-fitted  for  carrying  a  large 
beast  at  a  swift  speed,  and  is  s6  strong  a  weapon  of  de- 
fence that  an  active  donkey  can  kill  a  lion  with  a  well- 
delivered  kick. 

The  oldest  of  these  creatures  that  lead  to  the  horses  is 
called  Eohippus  or  beginning  horse.  This  fellow  had  on 
the  forefeet  four  large  toes,  each  with  a  small  hoof  and 
a  fifth  imperfect  one,  which  answered  to  the  thumb.  The 


HISTORY   OF   ORGANIC   LIFE. 


227 


hind  feet  had  gone  further  in  the  change,  for  they  each 
had  but  three  toes,  each  with  hoofs,  the  middle-toed  hoof 
larger  and  longer  than  the  others.  A  little  later  toward 
our  day  we  find  another  advance  in  the  Orohippus,  when 
the  little  imperfect  thumb  has  disappeared,  and  there  are 
only  four  toes  on  the  forefeet  and  three  on  the  hind. 

Yet  later  we  have  the  Mesohippus  or  half-way  horse. 
There  are  still  three  toes  on  the  hind  foot,  but  one  more 
of  the  fingers  of  the  forefeet  has  disappeared.  This  time 
it  is  the  little  finger  that  goes,  leaving  only  a  small  bone 
to  show  that  its  going  was  by  a  slow  shrinking.  The 
creature  now  has  three  little  hoofs  on  each  of  its  feet. 


Fiy.  104.    Development  of  Horse's  Foot. 

Still  nearer  our  own  time  comes  the  Miohippus,  which 
shows  the  two  side  hoofs  on  each  foot  shrinking  up  so 
that  they  do  not  touch  the  ground,  but  they  still  bear 
little  hoofs.  Lastly,  about  the  time  of  man's  coming  on 
the  earth,  appears  his  faithful  servant,  the  horse,  in  which 
those  little  side  hoofs  have  disappeared,  leaving  only  two 
little  "  splint "  bones  to  mark  the  place  where  these  side 
hoofs  belong.  Thus,  step  by  step,  our  horses'  feet  were 
built  up ;  while  these  parts  were  changing,  the  other  parts 
of  the  animals  were  also  slowly  altering.  They  were  at 
first  smaller  than  our  horses,  —  some  of  them  not  as  large 


228        EVENTS  ON  THE  EARTH'S  SURFACE. 

as  an  ordinary  Newfoundland  dog ;  others  as  small  as 
foxes. 

As  if  to  remind  us  of  his  old  shape,  our  horses  now 
and  then,  but  rarely,  have,  in  place  of  the  little  splint 
bones  above  the  hoof,  two  smaller  hoofs,  just  like  the  foot 
of  MioJiippus.  Sometimes  these  are  about  the  size  of  a 
silver  dollar,  on  the  part  that  receives  the  shoe  when 
horses  are  shod. 

In  this  way,  by  slow-made  changes,  the  early  mammals 
pass  into  the  higher.  Out  of  one  original  part  are  made 
limbs  as  different  as  the  feet  of  the  horse,  the  wing  of  a 
bat,  the  paddle  of  a  whale,  and  the  hand  of  man.  So 
with  all  the  parts  of  the  body  the  forms  change  to  meet 
the  different  uses  to  which  they  are  put. 

At  the  end  of  this  long  promise,  which  was  written  in 
the  very  first  animals,  comes  man  himself,  in  form  closely 
akin  to  the  lower  animals,  but  in  mind  immeasurably  apart 
from  them.  We  can  find  every  part  of  man's  body  in  a 
little  different  shape  in  the  monkeys,  but  his  mind  is  of 
a  very  different  quality.  While  his  lower  kindred  cannot 
be  made  to  advance  in  intelligence  any  more  than  man 
himself  can  grow  a  horse's  foot  or  a  bat's  wing,  he  is  con- 
stantly going  higher  and  higher  in  his  mental  and  moral 
growth. 

So  far  we  have  found  but  few  traces  of  man  that  lead 
us  to  suppose  that  he  has  been  for  a  long  geological  time 
on  the  earth,  yet  there  is  good  evidence  that  he  has  been 
here  for  a  hundred  thousand  years  or  more.  It  seems 
pretty  clear  that  he  has  changed  little  in  his  body  in 
all  these  thousands  of  generations.  The  earliest  remains 
show  us  a  large-brained  creature,  who  used  tools  and 
probably  had  already  made  a  servant  of  fire,  which  so 
admirably  aids  him  in  his  work. 


HISTORY   OF   ORGANIC   LIFE.  229 

Besides  the  development  of  this  wonderful  series  of 
animals,  that  we  may  call  in  a  certain  way  our  kindred, 
there  have  been  several  other  remarkable  advances  in  this 
Tertiary  time,  this  age  of  crowning  wonders  in  the  earth's 
history.  The  birds  have  gone  forward  very  rapidly ;  it  is 
likely  that  there  were  no  songsters  at  the  first  part 
of  this  period,  but  these  singing  birds  have  developed 
very  rapidly  in  later  times.  Among  the  insects  the  most 
remarkable  growth  is  among  the  ants,  the  bees,  and  their 
kindred.  These  creatures  have  very  wonderful  habits ; 
they  combine  together  for  the  making  of  what  we  may 
call  states,  they  care  for  their  young,  they  wage  great 
battles,  they  keep  slaves,  they  domesticate  other  insects, 
and  in  many  ways  their  acts  resemble  the  doings  of  man. 
Coming  at  about  the  same  time  as  man,  these  intellectual 
insects  help  to  mark  this  later  stage  of  the  earth  as  the 
intellectual  period  in  its  history.  Now  for  the  first  time 
creatures  are  on  the  earth  which  can  form  societies  and 
help  each  other  in  the  difficult  work  of  living. 

Among  the  mollusks,  the  most  important  change  is  in 
the  creation  of  the  great,  strong  swimming  squids,  the 
most  remarkable  creatures  of  the  sea.  Some  of  these  have 
arms  that  can  stretch  for  fifty  feet  from  tip  to  tip. 

Among  the  plants,  the  most  important  change  has  been 
in  the  growth  of  flowering  plants,  which  have  been  con- 
stantly becoming  more  plenty,  and  the  plants  which  bear 
fruits  have  also  become  more  numerous.  The  broad- 
leaved  trees  seem  to  be  constantly  gaining  on  the  forests 
of  narrow-leaved  cone-bearers,  which  had  in  an  earlier 
day  replaced  the  forests  of  ferns. 

In  these  Tertiary  ages,  as  in  the  preceding  times  of  the 
earth,  the  lands  and  seas  were  much  changed  in  their 


230       EVENTS  ON  THE  EARTH'S  SURFACE. 

shape.  It  seems  that  in  the  earlier  ages  the  land  had 
been  mostly  in  the  shape  of  large  islands  grouped  close 
together  where  the  continents  now  are.  In  this  time, 
these  islands  grew  together  to  form  the  united  lands  of 
Europe,  Asia,  Africa,  Australia,  and  the  twin  American 
continents ;  so  that,  as  life  rose  higher,  the  earth  was 
better  fitted  for  it.  Still  there  were  great  troubles  that 
it  had  to  undergo.  There  were  at  least  two  different 
times  during  the  Tertiary  age  termed  glacial  periods, 
times  when  the  ice  covered  a  large  part  of  the  northern 
continents,  compelling  life  of  all  sorts  to  abandon  great 
regions,  and  to  find  new  places  in  more  southern  lands. 
Many  kinds  of  animals  and  plants  seem  to  have  been  de- 
stroyed in  these  journeys;  but  these  times  of  trial,  by 
removing  the  weaker  and  less  competent  creatures,  made 
room  for  new  forms  to  rise  in  their  places.  All  advance  in 
nature  makes  death  necessary,  and  this  must  come  to 
races  as  well  as  to  individuals  if  the  life  of  the  world  is 
to  go  onward  and  upward. 

Looking  back  into  the  darkened  past,  of  which  we  yet 
know  but  little  compared  with  what  we  would  like  to 
know,  we  can  see  the  great  armies  of  living  beings 
led  onward  from  victory  to  victory  toward  the  higher 
life  of  our  own  time.  Each  age  sees  some  advance, 
though  death  overtakes  all  its  creatures.  Those  that  es- 
cape their  actual  enemies  or  accident  fall  a  prey  to  old 
age:  volcanoes,  earthquakes,  glacial  periods,  and  a  host  of 
other  violent  accidents  sweep  away  the  life  of  wide  re- 
gions, yet  the  host  moves  on  under  a  control  that  lies 
beyond  the  knowledge  of  science.  Man  finds  himself 
here  as  the  crowning  victory  of  this  long  war.  For  him 
all  this  life  appears  to  have  striven.  In  his  hands  lies  the 


HISTORY   OF   ORGANIC   LIFE.  231 

profit  of  all  its  toil  and  pain.  Surely  this  should  make 
us  feel  that  our  duty  to  all  these  living  things,  that  have 
shared  in  the  struggle  that  has  given  man  his  elevation,  is 
great,  but  above  all  great  is  our  duty  to  the  powers  that 
have  been  placed  in  our  bodies  and  our  minds. 


APPENDIX. 


CRYSTALLINE  ROCKS. 

/^vUR  rapid  glance  at  the  machinery  of  the  world  has 
^-^  shown  us  some  little  of  most  of  the  great  engines 
that  are  at  work  within,  upon,  or  without  it,  —  engines 
that  make  it  the  wonderful  workshop  that  it  is.  Let  us 
now  turn  back  to  see  some  of  the  lower,  but  still  more 
important,  portions  of  its  mechanism  which  are  given  to 
us  in  that  part  of  inorganic  nature  known  as  the  kingdom 
of  crystalline  forms. 

First,  let  us  notice  that  nearly  all  substances  in  nature 
have  three  states  of  existence :  the  gaseous,  the  fluid,  and 
the  solid.  We  are  familiar  with  these  three  shapes  of 
water  because  there  is  only  a  little  difference  of  tempera- 
ture needed  to  carry  it  through  all  the  stages.  Over  a 
fire,  a  lump  of  ice  will  quickly  become  fluid,  and  in  a 
short  time  it  will  pass  into  steam,  as  we  are  accustomed 
co  term  its  gaseous  state.  We  do  not  commonly  see  this 
behavior  in  other  substances,  because,  in  iron,  for  instance, 
the  temperature  necessary  to  carry  it  from  the  solid, 
through  the  fluid,  to  the  gaseous  state,  is  perhaps  thirty 
or  forty  times  as  great  as  is  required  to  pass  water  through 
these  stages.  It  is  now  believed  that  all  simple  sub- 
stances, such  as  our  metals,  and  a  great  many  of  the  more 
complicated  substances,  made  up  by  the  union  of  several 
simple  substances,  can  exist  in  these  three  conditions;  so 
that  we  may  accept  it  as  a  general  truth  in  nature  that 


234  APPENDIX. 

substances  have  usually  the  three  possible  states  of  solid, 
fluid,  and  gas. 

While  in  the  state  of  gas  or  fluid,  all  matter  seems  to 
remain  in  a  uniform  shapeless  condition  ;  but  when  the  sub- 
stance becomes  solid,  it  generally  enters  into  the  crystalline 
form.  The  best  way  to  get  an  idea  of  this  peculiar  condi- 
tion is  to  examine  a  number  of  crystalline  substances,  as, 
for  instance,  salt,  sugar,  alum,  quartz,  etc.  Every  day  we 
come  in  contact  with  a  dozen  or  more  out  of  the  thou- 
sands of  substances  that  take  this  shape. 

If  we  look  closely  at  crystals  of  one  substance,  we  see 
that  they  have  the  same  form,  or  have  shapes  that  arise 
from  slight  changes  of  a  particular  form.  For  instance, 
crystals  of  common  salt  have  one  shape,  while  crystals 
of  quartz  have  a  very  different  shape.  The  number  of 
sides  and  the  slope  of  these  sides  to  each  other  give  the 
peculiar  forms. 

We  do  not  know  what  causes  different  substances  to 
take  these  different  forms,  but  we  do  know  that  from  the 
beginning  of  the  earth  each  substance  has  its  form,  and 
that  they  are  the  same  for  all  time.  Further  than  this, 
the  meteoric  stones  that  fall  from  the  heavens  show  us 
that  the  same  rules  of  form  affect  the  substances  in  the 
other  planets  of  our  solar  system  or  other  solar  systems, 
whence  it  is  supposed  that  these  stones  come. 

The  rules  that  control  the  forms  of  these  crystals  and 
make  them  the  subject  of  the  science  of  crystalography 
are  very  interesting,  but  the  matter  is  too  difficult  for  dis- 
cussion here.  These  rules  are  so  precise  that  this  subject 
is  really  a  branch  of  geometry  as  well  as  a  part  of  chem- 
istry and  geology.  * 

We  must  next  notice  that  if  we  examine  the  rocks  of 
the  earth's  surface,  we  find  that  a  part  of  them  belong  to 


CRYSTALLINE   ROCKS.  235 

the  class  of  stratified  deposits,  and  generally  show  no  signs 
of  crystalline  minerals  except  in  cracks  which  have  evi- 
dently been  filled  in  by  the  action  of  water.  Such  rocks 
are  generally  distinctly  bedded,  and  show  us  that  they 
have  been  little  changed  since  they  were  formed  on  the 
bottoms  of  old  seas  or  lakes. 

Then  there  is  another  class  of  rocks,  called  "crystal- 
line," from  the  fact  that  crystals  abound  all  through  their 
masses.  These  rocks  we  suppose  to  have  been  stratified 
rocks  that  have  been  so  much  heated  that  the  particles 
were  free  to  move  together  as  they  pleased,  and  so  have 
gathered  into  the  crystalline  form.  This  heat  may  have 
actually  melted  the  rocks,  as  was  the  case  with  some  of 
our  granites  ;  or,  the  rocks  having  been  made  very  hot,  the 
water  they  held  in  their  interstices  was  able  to  dissolve  the 
various  minerals,  and  so  make  them  free  to  take  on  the 
shape  of  crystals.  When  a  mass  of  limestone  is  deeply 
buried  in  the  earth,  it  becomes  heated  because  it  is 
brought  near  the  hot  interior  of  the  earth,  and  the  water 
that  is  contained  in  it  dissolves  the  lime,  and  so  enables 
the  crystals  of  lime  carbonate  to  form.  In  this  way,  our 
rocks  made  of  limestone  mud  may  be  changed  to  crys- 
talline marble,  its  different  ingredients  being  gathered 
together  into  their  several  peculiar  crystals. 

When  these  stratified  rocks,  which  were  once  lime- 
stones, mud,  sand,  and  gravel,  have  their  various  sub- 
stances changed  into  crystals,  the  rocks  then  become  very 
different  from  what  they  were  before.  The  alteration  is 
often  so  great  that  we  cannot  say  what  the  rock  was 
before  the  change  came  upon  it. 

It  is  from  the  action  of  the  crystallizing  forces  on  rocks 
that  the  most  puzzling  changes  are  brought  about,  and  the 
science  of  mineralogy  comes  to  exist.  The  principal  un- 


236  APPENDIX. 

crystallized  rocks  are  named  from  their  evident  characters, 
independent  of  any  crystals  they  may  contain.  They  are 
made  up  of  various  substances,  which  will  be  described 
under  their  names  and  with  their  crystalline  forms. 

We  have  already  considered  these  familiar  uncrystal- 
line  rocks  ;  we  will  now  recall  them,  and  give  a  statement 
of  the  changes  that  heat  and  other  metamorphic  agents  may 
bring  to  them. 

Claystone  or  Clay  Slate.  Made  of  fine  mud  particles. 
It  may  be  principally  of  clay,  or  partly  of  lime  or  quartz. 
It  may  contain  some  carbon,  as  in  the  shales  near  the 
coals.  Useful  for  building-stones  or  flagging,  etc. ;  or,  when 
in  the  shape  of  true  slate,  for  roofing  houses,  for  which  its 
thin,  leaf-like  sheets  are  well  fitted.  The  peculiar  struc- 
ture of  roofing-slate  is  called  slaty  cleavage,  because  it  is 
found  only  in  rocks  of  this  description,  never  in  limestones 
or  the  coarse-grained  rocks.  This  cleavage  is  produced  in 
the  following  way.  The  slate  rock  is  made  up  of  small 
bits  of  many  different  stones,  little  fragments  of  quartz, 
of  feldspar,  etc.  Among  these  substances  there  are  gener- 
ally very  numerous,  though  very  small,  flakes  of  mica. 
These  bits  of  mica  are  always  very  thin,  generally  a  dozen 
or  more  times  as  wide  as  they  are  thick.  When  the  rock 
was  built  in  its  first  form  as  a  soft  mud,  these  flakes  fell 
upon  the  bottom  in  many  different  positions,  so  that  their 
long  faces  lie  in  all  sorts  of  ways.  When  the  rock  hardens, 
they  seem  to  bind  it  together,  somewhat  as  the  hair  holds 
the  plasterer's  mortar  together.  Now,  if  it  happens  that 
the  rock  filled  with  these  mica  flakes  is  very  much 
squeezed,  as  rocks  are  when  they  are  forced  together  by 
the  mountain  building  forces,  it  may  hg  forced  to  stretch 
itself  out  in  any  direction,  like  dough  under  the  cook's 
rolling-pin.  We  can  easily  see  that  these  several  mica 


CBYSTALLHTE   BOCKS.  237 

flakes  will  then  all  lie  in  about  the  same  direction.  Per- 
haps this  will  be  more  easily  seen  if  we  imagine  the  flakes 
of  mica  mingled  in  dough  and  then  rolled  out.  The 
result  will  be  that  their  longer  faces  will  generally  lie 
parallel  with  the  surface  of  the  flattened  cake.  It  is 
easy  to  imagine  that  when  all  these  flakes  are  turned  by 
the  stretching  of  the  rock,  so  that  their  planes  are  par- 
allel to  each  other,  the  rock  will  split  much  more  easily 
along  the  line  of  their  faces  than  it  will  across  them.  It 
is  this  adjustment  of  mica  planes  that  causes  our  common 
roofing  slate  to  split  so  easily  into  thin  sheets. 

This  slaty  cleavage  is  the  simplest  of  the  changes  that 
come  over  clay  stone  when  it  enters  into  the  great  labora- 
tory beneath  the  earth's  surface  by  its  burial  beneath 
other  rocks.  If  it  is  deeply  buried,  if  ten  or  twenty  thou- 
sand feet  of  rocks  are  laid  down  upon  it,  it  may  undergo 
very  great  changes.  Thus  deeply  buried,  it  becomes  very 
much  heated  by  the  inner  heat  of  the  earth.  This  affords 
the  particles  of  the  rock  a  chance  to  become  dissolved  in 
water  and  rearranged  in  the  crystalline  form.  This  gives 
us  a  mica  schist,  or  other  similar  rock,  in  place  of  the 
original  slate.  If  still  further  heated,  so  that  the  rock 
melts,  the  mass  may  become  a  trap-like  rock,  and  lose  all 
trace  of  its  original  structure  and  character. 

Limestones  and  Limestone  Marbles.  When  limestones  are 
subjected  to  the  action  of  heated  water,  the  rock  becomes 
more  solid,  the  fossils  are  dissolved  away,  and  the  whole 
mass  takes  on  a  more  or  less  crystalline  form.  These  crys- 
tals are  generally  of  lime  carbonate,  but  sometimes  of 
lime  sulphate  or  gypsum,  or  other  salts  of  lime.  In  this 
changed  form,  limestone  affords  the  greater  part  of  the 
polished  stone  used  in  building  and  for  table-tops,  etc. 

Sandstones.     Heat  and  heated  water  work   to  change 


238  APPENDIX. 

sandstones  into  more  compact  rocks,  termed  "  quartzites." 
In  these  rocks  we  can  no  longer  see  the  distinct  grains  of 
sand,  but  the  whole  is  converted  into  a  rather  solid  mass 
of  flinty  matter.  The  grains  of  sand  are  taken  to  pieces 
in  the  heated  water  and  re-made  so  that  the  crystals  are 
all  close  set  and  locked  together. 

In  these  changes  of  claystones,  limestones,  and  sand- 
stones, the  alteration  is  so  slight  that  the  mass  is  still  dis- 
tinctly a  bedded  rock.  But  the  changes  may  go  still 
further.  The  rocks  may  be  so  kneaded  together  by  the 
strong  movements  that  take  place  in  the  depths  of  the 
earth  that  the  bedding  which  so  distinctly  marked  the  wa- 
ter origin  of  the  material  can  no  longer  be  traced.  It  also 
happens  that  other  chemical  substances,  besides  those  origi- 
nally in  the  rock,  are  gradually  brought  in  by  the  perco- 
lating waters,  so  that  the  chemical  nature,  as  well  as  the 
shape,  of  the  mass  is  changed.  It  is  probably  in  this  way 
that  a  host  of  rocks,  which  are  termed  "gneisses,"  "gran- 
ites," and  "syenites,"  are  formed.  In  some  cases  we  can 
still  trace  a  remnant  of  the  bedding  of  these  greatly 
changed  rocks,  enough  to  show  that  they  were  originally 
made  on  sea-floors  as  stratified  deposits. 

If  the  heat  or  the  action  of  heated  water  still  further 
affect  the  rocks,  they  may  take  on  either  of  two  other 
shapes.  They  may  be  converted  into  dykes  or  into  veins. 

Dykes  are  formed  when  the  rock  is  so  heated  that  it 
more  or  less  completely  melts.  In  this  melting,  it  is  aided 
by  the  water  that  all  rocks  contain.  In  this  melted  state, 
it  is  squeezed  into  crevices  of  other  rocks,  as  before  de- 
scribed. This  trap  matter  is  generally  highly  crystallized, 
and,  of  course,  has  lost  all  trace  of  its  stratification. 

Veins  are  deposits  of  matter  nearly  always  in  the  crys- 
tallized form,  where  the  carriage  of  the  matter  into  a 


CRYSTALLINE  ROCKS.  239 

crevice  has  been  brought  about  by  the  action  of  water, 
which  first  dissolves  the  substances,  and  then  allows  them 
to  deposit  as  crystals.  In  the  several  ways  above  de- 
scribed, a  great  variety  of  crystals  is  formed,  and  from  the 
association  together  of  different  crystals  a  great  many  rocks 
are  made. 

Of  these  crystals,  which  altogether  amount  to  several 
hundred  species  or  kinds,  the  following  are  the  most  im- 
portant and  the  most  common  in  rocks. 

1.  Quartz,  by  far  the  commonest  crystals  found  on  the 
earth.     Almost  all  sand  consists  of  broken  crystals  of  this 
substance.     Its  usual  form  is  that  of  a  six-sided  prism, 
with  a  six-sided  pyramid  at 

the  end.     Sometimes  there  is 
a  pyramid  at  each  end.     It 
also,  but  very  rarely,  crystal- 
lizes six-sided  tables.  Ordina- 
rily, these  crystals  are  trans- 
parent and  glass-like,  but  they 
may  be  colored  of  many  tints, 
as  of  a  violet  or  amethyst 
color.     They  are  always  too      **ff- 105-  Quartz>  common  forms, 
hard  to   be   scratched   by  steel.      Quartz   is  very  often 
found  in  the  uncrystallized  form,  as  in  flint,  agate,  chal- 
cedony, etc. 

2.  Feldspar.     This  is,  next  after  quartz,  the  commonest 
crystal  in  the  rocks.     It  is  about  as  heavy  and  as  hard 
as  quartz,  —  about  two  and  one-half  times  the  weight  of 
water.     Its  crystals  split  in  two  directions,  breaking  easily 
into  parallelograms,  with  smooth,  waxy-looking,  lustrous 
sides,  while  quartz  crystals  do  not  split  in  this  fashion. 
The  crystals  vary  so  much  in  form  that  they  cannot  be 
represented  here. 


240 


APPENDIX. 


3.  Mica.  This  is  a  very  common  crystal,  which  easily 
splits  in  thin,  elastic  flakes.  Sometimes  the  crystals  are 
as  transparent  as  glass,  but  more  commonly  they  are 
yellow,  wine-colored,  green,  or  smoky  in  hue.  Commonly, 
the  crystals  are  small,  as  in  granites,  but  when  occurring 
in  veins  they  are  sometimes  a 
foot  or  more  across.  Flakes 
from  these  large  crystals  are 
used  for  stove  windows,  for 
covering  photographs,  or  for 
the  battle  lanterns  and  win- 
dows of  our  ships,  where  glass 
would  be  broken  by  the  jar  of 
guns  or  of  the  enemies'  shot. 
Fit/,  loe.  Mica.  This  substance  may  easily  be 

distinguished  from  all  others  by  the  fact  that  undecayed 
crystals  will  always  yield  elastic  flakes  when  divided  with 
the  knife.  The  thin  flakes  broken  from  mica  crystals  are 
very  buoyant  and  float  far  in  the  water.  They  may  be 
seen  glistening  in  most  sandstones. 

Hornblende.  Next  after  the  three  above  named,  one  of 
the  commonest  minerals  is 
hornblende.  It  is  very  vari- 
able in  all  its  qualities.  It 
may  take  the  shape  of  oblong 
prisms,  of  tufts,  of  crystals, 
or  of  hair-like  fibres  laid  close 
together.  Sometimes  these 
fibres  are  so  long  and  elastic 
that  they  may  be  spun  and 
woven  like  cotton.  In  this 
shape,  the  mineral  is  termed  "  asbestos,"  which  means 
unburnable.  This  name  has  been  applied  to  it  because  it 


Fiy.  107. 
Hornblende,  common  forms. 


CRYSTALLINE   ROCKS. 


241 


has  been  used  in  making  a  cloth  which  is  quite  fireproof. 
Among  the  ancients,  such  cloth  was  sometimes  used  to 
wrap  the  dead  on  the  funeral  pyre,  so  that  the  ashes 
of  the  consumed  body  might  not  be  scattered. 

This  mineral  is  composed  of  the  elements  silica,  lime, 
magnesia,  and  iron. 

Pyroxene  is  closely  akin  to  hornblende  in  composition, 
but  the  crystals  have  the  form  shown  in  the  figure.  It  is 
never  fibrous,  nor  does  it  show  the  brush-like  crystals 
common  in  the  latter  mineral. 


Fig.  108.    Pyroxene.  Fig.  109.    Calcite. 

Calcite.  This  is  one  of  the  commonest  minerals.  It  is 
the  shape  taken  by  ordinary  limestone  or  lime  carbonate 
when  crystallized.  The  crys- 
tals have  the  form  shown  in 
the  diagrams.  They  are  soft, 
and  easily  scratched  with  a 
knife.  It  may  be  of  several 
different  colors,  and  is  often 
transparent.  It  is  composed 
of  44  parts  of  carbonic  acid 
and  56  of  lime. 

Dolomite  is  akin  to  calcite,  Fiu- no-  Dolomite, 

from    which   it  differs  in  having   carbonate  of  magnesia 


242 


APPENDIX. 


along  with  carbonate  of  lime.  It  is  much  less  abundant 
than  calcite.  The  forms  of  the  crystals  are  shown  in  the 
figures. 

An  easy  test  for  these  minerals  is  made  by  dipping  them 
in  a  powdered  shape  into  muriatic  acid  diluted  with 
one-half  its  bulk  of  cold  water.  Calcite  will  cause  the 
mixture  to  foam  or  effervesce  freely  at  once,  while  it  will 
be  necessary  to  heat  the  acid  and  water  before  the  dolo- 
mite will  give  off  its  gas,  except  in  a  very  sparing  way. 

Gypsum  is  a  very  common  mineral.  It  is  a  combination 
of  sulphuric  acid  and  lime  with  water.  When  burnt,  it  is 
the  plaster  of  paris  of  the  arts,  much  used  in  making  casts 
of  statues  and  various  fine  mouldings.  It  occurs  in  two 
forms.  In  one,  it  is  combined  with  some  water,  when  it 
crystallizes  in  the  shape  shown  by  Fig.  111.  In  the  other, 
it  is  without  any  water  in  its  combination,  when  it  takes  a 
rectangular  shape. 


Fig.  111.    Gypsum.  Fig.  112.    Common  Salt. 

Common  Salt.  This  is  a  compound  of  sodium  and  chlo- 
rine. Its  crystals  have  the  form  shown  in  the  figures.  It 
often  makes  beds  hundreds  of  feet  in  thickness.  In  this 
form,  it  is  generally  of  a  brownish  color,  and  only  partly 
transparent;  but  sometimes  this  rock  salt  is  as  transparent 
as  ice.  It  is  formed  wherever  salt  water  is  enclosed  in  a 


CRYSTALLINE   ROCKS. 


243 


basin,  where  it  receives  so  little  rain  water  that  it  evapo- 
rates. It  is  then  thrown  down  in  crystals  on  the  bottom. 
Salt  is  now  depositing  in  many  shallow,  land-locked  pools 
along  those  portions  of  the  seashore  that  have  little  rain, 
and  also  in  many  inland  seas  that  have  no  outlet,  as,  for 
instance,  in  the  Salt  Lake  of  Utah,  the  Dead  Sea  of  Asia, 
etc.  There  were  certain  periods  in  the  past  history  of  the 
earth  when  salt  was  very  extensively  deposited.  They 
were  probably  the  times  of  least  rainfall. 

The  foregoing  are  the  commonest  crystalline  minerals 
of  the  rocks.  There  are  others,  which,  though  less  fre- 
quently found,  are  still  common,  and  should  be  recognized 
by  the  student.  First  among  these,  we  may  notice  certain 
ores  of  the  important  metals.  It  will  be  noticed  that  all 
of  them  are  not  found  in  the  form  of  crystals. 

Pyrite,  or  Pyrites,  is  composed  of  sulphur  and  iron.  It 
commonly  has  a  light  yellow  hue,  which  causes  it  to  be 
often  mistaken  for  gold,  whence  it  receives  the  popular 
name  of  "fools'  gold."  Its 
crystals  are  shaped  as  in  Fig. 
113.  These  crystals,  when  ex- 
posed to  the  air,  quickly  take 
up  oxygen,  and  rust  or  burn 
sometimes  with  such  rapidity 
that  they  give  an  intense  heat. 
As  they  often  occur  in  large 
quantity  in  coal,  their  burning 
frequently  fires  coal-mines  or 
ships  laden  with  the  coal.  Hundreds  of  ships  have  been 
lost  in  this  way.  By  allowing  these  crystals  to  burn, 
sulphuric  acid  may  be  produced. 

Magnetite.  This  is  a  crystalline  ore  of  iron,  occurring 
in  the  shapes  shown  in  the  figure.  It  is  of  a  grayish  or 


244  APPENDIX. 

blackish  color.  The  peculiarit}'  which  distinguishes  it  from 
other  minerals,  is  that  the  crystals  strongly  attract  the 
magnetic  needle.  This  min- 
eral occurs  both  in  beds  and 
in  veins.  It  is  as  yet  not 
known  what  causes  the  mag- 
netic character.  It  may  be 
due  to  the  action  of  heat.  A 
large  part  of  the  iron  now 
in  use  is  derived  from  mag- 
netite. 

Fig.  114.  Magnetite.  Hematite,  so  named   from 

its  blood-red  color,  is  sometimes  found  in  crystals,  but 
more  often  in  the  massive  form.  It  generally  occurs  in 
beds.  It  stains  the  hand  red,  and  is  hence  frequently 
called  "  dye-stone  ore."  This  ore  is  often  fossiliferous,  the 
fossil  shells,  etc.,  having  been  converted  into  the  iron  oxide. 
It  is  composed  of  two  parts  of  iron  to  three  of  oxygen. 

Limonite  is  much  like  the  preceding,  except  that  it  does 
not  occur  in  crystals,  and  is  of  a  brownish  or  yellowish 
color.  It  may  be  formed  by  the  combination  of  water 
with  the  hematite  ore. 

Hematite  and  limonite  are  often  found  together  as  dis- 
tinctly bedded  iron  ores.  The}'  represent  the  little- 
changed  iron  ores  that  are  often  found  interbedded  in 
our  limestones,  sandstones,  and  slates. 

Siderite,  or  Iron  Carbonate,  is  a  combination  of  carbonic 
acid  and  iron,  and  is  made  by  the  infiltration  of  iron  ox- 
ide into  limestone  beds,  which  takes  away  a  part  of  the 
lime,  replacing  it  with  iron.  It  readily  decays,  so  that 
while  it  at  first  is  of  a  bluish  or  whitish  color,  and  looks 
like  limestone,  on  exposure  to  the  air  it  soon  becomes  a 
iimonite,  or,  in  some  cases,  a  hematite.  It  is  generally  in 


CRYSTALLINE   ROCKS. 


245 


massive,  stratified  form ;  but,  when  crystallized,  it  takes 
the  shapes  shown  in  the  figures. 


Fig.  115.    Siderite.  Fig.  116.    Metallic  Copper. 

Ores  of  Copper.  Copper  is  often  found  as  a  pure 
metal,  scattered  through  various  rocks  in  the  form  of 
grains  or  sheets.  Especially  is  it  abundant  in  this  form 
on  the  southern  shore  of  Lake  Superior.  In  its  metallic 
state,  it  is  sometimes  crystalline,  as  in  the  forms  shown  in 
the  figures.  More  commonly,  it  occurs  as  ore,  of  which 
the  following  is  the  most  important,  viz. :  — 

Copper  Pyrites,  or  Chalcopyrite,  composed  of  sulphur 
and  iron,  with  a  variable  proportion  of  copper.  It  is 
closely  related  to  iron  pyrites, 
and  differs  from  it  by  the 
presence  of  copper. 

There  are  many  other  ores 
of  copper  formed  by  its  mix- 
ture with  other  metals,  but 
the  principal  production  of 
copper  is  from  the  two  forms 
above  given. 

Lead.      This  substance   is  Fig.  in.  Galena, 

never  found  in  the  metallic  state.      Its  principal  ore  is 
galena,  or  lead  sulphate.     It  has  the  color  of  lead  when 


246 


APPENDIX. 


the  crystals  are  fresh.  It  contains  13  per  cent  of  sulphur. 
It  always  occurs  in  crystals  that  have  the  form  given  in 
the  figure.  It  is  commonly  found  in  veins,  but  sometimes 
in  beds,  where  the  galena  has  been  gathered  in  the  shape  of 
obscure  veins.  The  crystals  have  the  shape  shown  in  the 
figure.  They  are  easily  split  along  the  sides  of  the  crystals. 
Lead  generally  contains  more  or  less  silver,  and  a  large 
part  of  the  silver  of  the  world  is  extracted  from  galena. 

Silver  occurs  in  the  form 
of  various  oxides,  but  some- 
times it  is  found  in  the  metal- 
lic form  as  threads  or  sheets 
running  through  the  rock. 
When  crystallized,  its  crystals 
have  the  form  shown  in  the 
figure.  The  principal  ores  of 
silver  are  formed  by  combina- 
Fiy.  n«.  Silver.  tions  with  sulphur,  bromine, 

chlorine,    but   its    commonest   form    of  occurrence   is   in 
mixture  with  galena  or  with  copper  ores. 

Zinc.  This  metal  is,  like  lead,  not  naturally  found  in 
the  metallic  state.  Its  com- 
mon form  of  occurrence  is  in 
the  shape  of  sphalerite  or 
zinc  blende,  a  combination  of 
33  parts  of  sulphur  and  67 
of  zinc.  The  crystals  are  ot 
various  colors,  from  yellow 
to  black.  When  powdered, 
they  give  a  white  dust.  The 
*%.H9.  Sphalerite.  crystalline  forms  are  shown 

in  the  figures.     This  metal  is  frequently  associated  with 
lead  in  ordinary  veins  or  veinlets  in  bedded  rocks. 


CRYSTALLINE   KOCKS. 


247 


Tin.  This  is  one  of  the  rarest  metals  in  America,  being 
the  only  one  of  the  important  metals  that  has  never  been 
profitably  mined  in  this  country.  It  is  generally  found  in 
the  shape  of  thin  veins  in  granite  rocks.  Its  only  impor- 
tant form  is  that  of  cassiterite  or  tin  oxide,  in  which  shape 


Fir/.  120.   Cassiterite.  Fig.  121.  Streamer  Nugget  Gold. 

it  is  a  dark-brownish,  very  heavy,  ore.  The  crystals  are 
found  in  the  shapes  shown  in  the  figure.  These  crystals 
do  not  easily  dissolve  ;  so,  when  the  rock  wears  away,  they 
often  are  gathered  in  the  river-beds  like  gold  and  plati- 
num, and  are  called  "  stream  tin."  The  most  of  the  tin  of 
commerce  has  been  collected  in  this  way. 

G-old.  This  metal  is,  with  the  possible  exception  of 
platinum,  the  metal  that  is 
least  disposed  to  combine  with 
other  substances.  It  is  there- 
fore generally  found  in  the 
metallic  state,  usually  in  the 
form  of  grains,  sheets,  or 
fibres  in  the  rocks  or  in  the 
sands  of  rivers.  Though  the 
most  sparingly  accumulated 
in  masses  of  all  metals,  it  is  ^'122'  Crystals  of  Gold, 
perhaps  the  most  generally  disseminated  of  all.  The  most 


248 


APPENDIX. 


of  our  clays  and  sands  contain  traces  of  it.  In  its  crys- 
talline shapes,  which  it  rarely  assumes,  it  has  the  forms 
shown  in  the  figure. 

Aluminum.  This  metal  is  never  found  in  the  metallic 
state,  though  it  is  perhaps  the  most  plentiful  of  all  the 
metals  that  could  be  used  by 
man  in  his  arts.  In  its  ordi- 
nary form,  it  exists  as  a  com- 
pound of  alumina  and  silic 
oxide,  and  is  a  most  important 
element  in  all  our  common 
clays.  This  metal  is  of  a  sil- 
very-white color ;  it  is  won- 
derfully light,  being  scarcely 

Fig.  123.  Corundum.  heavier  than  heavy  wood,  and 

remarkably  strong.  But  for  the  fact  that  it  is  exceedingly 
costly  to  reduce  it  to  the  form  of  a  metal,  it  would  be  perr 
haps,  after  iron,  the  most  important  of  all  to  man. 

Sulphur.     This  substance  plays  a  large  part  in  the  geo- 
logical world.     It  is  rarely  found  in  the  crystalline  form, 


Fig.  124.    Sulphur. 

Fig.  125.    Baryta. 

except  in  the  neighborhood  of  volcanoes.  The  crystals 
have  the  well-known  resinous-looking  yellow  color.  They 
have  the  shapes  shown  in  the  figures. 


CRYSTALLINE    BOCKS. 


249 


There  are  several  other  less  important  crystals  that  may 
be  mentioned.  Among  these  barytes,  or  heavy  spar,  a 
compound  of  sulphuric  acid  and  baryta,  is  the  heaviest  of 
the  crystals  after  those  of  metallic  substances.  It  has  the 
form  shown  in  Fig.  125.  Fluorite,  or  fluor-spar,  a  com- 
pound of  fluorine  and  calcium,  is  one  of  the  handsomest  of 
our  crystals.  Its  colors  range  from  white  to  blue  or  yel- 
low. See  Fig.  126.  Arrogonite,  a  form  of  lime  carbonate, 
gives  crystals  shown  in  Fig.  127. 


.  126.   Fluorite. 


Fig.  127.    Arrogonite. 


When  certain  of  the  foregoing  crystals  are  associated 
together  in  a  mass  of  rock,  the  rock  receives  particular 
names,  according  to  the  crystalline  substances  that  enter 
into  its  composition.  Of  these  rocks,  named  from  the 
crystals  they  contain,  the  following  are  the  most  im- 
portant. 

G-ranite,  composed  of  intermingled  crystals  of  quartz, 
feldspar,  and  mica,  irregularly  crowded  together.  The 
proportion  of  the  several  sorts  of  crystals  may  vary,  as 
well  as  the  forms  of  the  crystals  themselves. 

Syenite  is  a  name  given  to  rock  composed,  like  granite, 
in  part  of  quartz  and  feldspar  crystals,  but  having  some 
form  of  hornblende  crystals  in  place  of  mica. 

Gneiss.     When  the  rock  has  the  crystals  crowded  to 


250  APPENDIX. 

gether  in  a  banded  form,  the  rock  is  called  "a  gneiss." 
In  some  cases,  this  banded  arrangement  is  the  remains  of 
stratification  planes  that  once  marked  the  rock  in  a  dis- 
tinct way  as  a  water-made  deposit.  If  the  mica  crystals 
are  present,  it  is  called  a  "  granitic  gneiss  " ;  if  the  horn- 
blende crystals  are  present,  it  is  called  a  "  syenitic 
gneiss." 

Mica  Schist.  When  the  mica  plates  are  very  abundant, 
and  the  feldspar  less  considerable,  the  rock  becomes  very 
easily  splitable,  and  shines  all  over  from  the  reflection  of 
the  mica  plates.  It  is  then  called  a  "  mica  schist."  When 
the  hornblende  is  abundant,  it  is  called  a  "hornblende 
schist." 

Porphyry.  This  is  a  name  given  to  any  rock  when 
there  is  a  cementing  mass  of  feldspar  or  quartz  in  which 
distinct  crystals  of  feldspar,  or  feldspar  and  quartz,  are 
lodged.  There  are  very  many  kinds,  and,  as  most  of 
them  are  handsome  when  polished,  they  have  been  much 
used  for  decorative  stones. 

The  following-named  rocks  are  not  crystalline.  They 
are  found  in  association  with  the  crystalline  rocks,  and 
deserve  the  attention  of  the  beginner  in  geology. 

Steatite,  or  fioapstone,  a  rock  largely  composed  of  mag- 
nesia, generally  of  a  mottled,  greenish-white  color,  thick 
bedded  or  entirely  massive.  It  has  a  curious  soapy  feel. 
Much  used  in  making  stoves,  fire-backs,  and  in  other 
places  where  heat  must  be  endured. 

Serpentine.  Also  largely  composed  of  magnesia,  and 
much  resembling  soaps  tone,  except  it  feels  less  soapy. 
Like  soapstone,  it  is  easily  cut  with  the  saw.  It  is  more 
mottled  than  soapstone,  takes  a  good  polish,  is  generally 
of  a  beautiful  greenish  co^,  and  hence  is  much  used  for 
decorative  purposes. 


CRYSTALLINE   ROCKS.  251 

Quartzite.  This  is  a  sandstone  that  has  had  its  grains 
more  closely  cemented  together  than  in  ordinary  sand- 
stones. Sometimes  the  grains  are  so  blended  that  they 
are  no  longer  visible.  In  this  shape,  it  is  often  called 
"chert,"  or  "flint."  Sometimes,  by  changes  which  we  do 
not  understand,  the  quartzite  becomes  flexible,  so  that  a 
slender  piece  can  be  bent  in  the  hand.  It  is  then  called 
Itacolumite,  from  a  mountain  in  Brazil,  where  it  was 
first  found.  It  occurs  plentifully  in  North  and  South 
Carolina. 

There  are  many  hundred  forms  of  crystals,  and  some 
score  of  rocks,  composed  in  larger  or  smaller  part  of  these 
crystals,  which  are  not  mentioned  here,  for  the  reason 
that  they  are  not  of  common  occurrence  on  the  earth's 
surface.1  The  most  important  of  these  omissions  is  the 
series  of  volcanic  rocks.  These  are,  it  is  generally  be- 
lieved, the  ordinary  stratified  rocks,  that  have  been  com- 
pletely melted  and  driven  up  to  the  surface.  Their  varia- 
tions are  due  in  part  to  the  original  chemical  nature  of 
the  rocks,  and  in  part  to  the  way  in  which  they  have 
cooled  from  their  melted  state. 

In  general,  we  may  say  that  the  crystalline  rocks  repre- 
sent those  portions  of  the  earth's  crust  which  have  been 
the  most  changed  by  heat,  acting  directly  or  through  hot 
water,  that  penetrates  the  rocks.  When  the  crystalline 
rocks  wear  down,  their  crystals  are  generally  broken  to 
pieces,  and  go  to  make  mudstones,  sandstones,  or  lime- 
stones, to  be  again  gathered  into  crystals  when  they  are 
deeply  buried  in  the  earth's  crust,  and  so  exposed  to  the 
action  of  heat. 

1  For  further  information  concerning  crystals,  see  Professor  J.  D.  Dana's 
System  of  Mineralogy,  5th  edition,  New  York,  1873 ;  also  his  Manual  of 
Geology,  New  York,  1880,  from  which,  in  part,  this  brief  account  is  taken. 


252  APPENDIX. 

Thus  we  see  that  the  rocks,  and  the  minerals  found  in 
them,  revolve  in  an  eternal  circle  by  the  action  of  water. 
They  are  constantly  changing  into  the  condition  of  mud. 
When  they  have  long  been  buried  in  the  crust  of  the 
earth,  they  become  changed  to  the  crystalline  structure. 
Their  change  to  this  condition  is  largely  the  effect  of 
water  action.  As  the  lands  wear  down,  the  rocks  once 
again  pass  into  the  control  of  water,  and  are  returned  to 
the  sea-floor. 


INDEX. 


A. 

Advance  in  organic  creations,  155. 
^Etna,  94. 

African  deserts,  19. 
Age  of  earth,  203. 
Air,  the,  56. 

heat-retaining  action,  59. 

currents,  99. 
Aluminium,  248. 
Ammonites,  170. 
Amphibians,  180. 

Animal  kingdom,  objects  sought,  162. 
Animals,  degradation  of,  200. 
Arno  River,  sand  of,  14. 
Articulates,  175. 
Artificial  stones,  32. 
Australia,  great  reef  of,  40. 


Barytes,  249. 
Birds,  181. 

with  tails,  222. 
Blue  Ridge,  section  from 
Bogs,  49. 

coal  from,  49,  50. 
Bomb,  bursting  of,  by  ice,  4. 

C. 

Calcite,  241. 
Cambrian,  213. 
Carbonic  acid  (CO2),  44. 
Carboniferous  period,  215. 
Cassiterite,  247. 
Caverns,  fossils  in,  84. 

life  of,  80. 

of  Kentucky,  85. 

sea-shore,  86. 

limestone,  75. 

volcanic,  85. 
Cephalopods,  170. 
Chalcopyrite,  245. 


Chili  shore,  changes  of,  14L 
Cincinnati  axis,  208. 
Classification,  150. 
Coal,  46. 

anthracite,  50. 

bituminous,  50. 

cannel,  50. 

of  different  regions,  53. 

period,  51. 

Richmond,  Va.,  51. 

seam,  52. 

use  of,  53. 

Colorado  cafion,  120. 
Conglomerate,  30. 
Connecticut,  119. 
Continents,  111. 
Copper,  ores  of,  245. 
Coral  reefs,  40. 
Cretaceous,  223. 
Crinoids,  43. 
Cross-bedding,  34. 
Crystalline  rocks,  233. 
Crustaceans,  176. 

D. 

Darwinian  Theory,  196. 

Degradation  among  animals,  200. 

Devonian,  215. 

Difference  and  relations  among  animals 

149. 

Dolomite,  241. 
Domesticated  animals,  199. 
Dromatherium,  219. 


Earth,  before  organic  life,  209. 
Earthquakes,  120. 

Lisbon,  131. 

of  Mississippi  Valley,  134. 

New  England,  134. 

Calif  ornian,  135. 

waves,  166. 


254 


INDEX. 


Earthworms,  action  of,  22. 
Echini,  166. 
Egypt,  sand  of,  19. 

mummies  of,  205. 
Kohippus,  226. 

Events  on  earth's  surface,  209. 
Expansion  in  freezing  of  water,  4. 

F. 

Falls  (water),  117. 

Niagara,  204. 

of  Ohio,  118. 
Felspar,  239. 
Fishes,  180. 
Fluorite,  249. 
Foraminifera,  42. 
Forests,  age  of,  47. 
Fossils,  formation  of,  189. 

conclusions  from,  193. 

G. 

Gasteropoda,  199. 
Glacial  pebbles,  10. 

scratches,  10. 
Glaciers,  8. 

extent  of,  11. 
Gneiss,  249. 
Gold,  247. 
Gulf  Stream,  103. 
Gypsum,  242. 

H. 

Heat  of  iron,  99. 

Hills,  107. 

History  of  earth,  209. 

organic  life,  240. 
Holothurians,  167. 
Hot  springs,  68. 

I. 

Insects,  176. 
Instincts,  177. 
Iron  carbonate,  244. 
Iron  pyrite,  etc.,  243. 

J. 

Jamaica,  earthquake  of,  132. 
Japan  current,  105. 
Jurassic  period,  223. 


Kentucky,  caverns  in,  76. 


Lakes,  125. 

salt,  125. 

glacial,  127. 
Lava,  94. 

Californian,  94. 
Lead,  245. 
Life,  work  of,  146. 
Limestone,  23,  38. 

fertility  from,  45. 
Limonite,  244. 
Lisbon  earthquake,  131. 
Lode,  Comstock,  69. 


Magnesite,  249. 

Magnetite,  243. 

Mammals,  182. 

Mammoth  Cave,  78. 

Marbles,  238. 

Mesohippus,  227. 

Metals,  method  of  deposition,  71. 

Mica,  240. 

schist,  250. 
Microlestes,  219. 
Millstone  grit,  30. 
Miohippus,  227. 
Mollusks,  168. 
Mountains,  108. 
Mud,  20. 

stones,  36. 

N. 
Nebular  hypotheses,  209. 

O. 

Ocean  currents,  102. 
Ohio  Falls,  118. 
Opossums,  183. 
Origin  of  life,  195. 
Oyster,  rate  of  growth,  39. 

P. 

Pebbles,  river,  1,  2,  3,  4. 

glacial,  8. 

sea,  5,  7. 

scratched,  32. 
Petroleum,  54. 
Plants,  advances  in,  158. 
Pliny,  death  of,  92. 
Porphyry,  250. 


INDEX. 


'255 


Pressure  (effects)  ,31, 
Proof  of  earth's  age,  203. 
Protozoa,  164. 
Pumice,  37. 
Pyrite,  243. 
Pyroxine,  241. 


Quartz,  239. 
Quartzite,  251. 


Q. 


it. 


Radiates,  164. 

Reptiles,  181. 

Richmond,  Va.,  coal,  51. 

Rivers,  114. 

Rocky  Mountains,  sand  in,  19. 

Roots  of  plants,  action  of,  23. 

effects  of,  31. 

rule  of  formatic 


Sahara,  19. 
Salt,  242. 
Salt  lakes,  125. 
Saltpetre  in  caverns,  85. 
Sand,  river,  12. 

sea-shore,  15. 
of  Arno  River,  14. 
of  Sahara,  19. 
polishing  by,  19. 
Sandstones,  34. 
Saturn's  rings,  210. 
Scyenite,  249. 
Sea  eggs,  166. 

cucumbers,  167. 

weeds,  157. 

pebbles,  6. 

beach,  7,  67. 

wearing  action  of,  142. 
Shrinkage  of  earth,  108. 
Siderite,  244. 
Silurian,  214. 
Silver,  246. 
Soapstone,  250. 


Soils,  24. 

structure  of,  24,  25. 

working  of,  26. 

action  of  man  on,  27. 

glacial,  28. 

of  Virginia,  29. 
Species,  how  made,  195. 
Stalactites,  78. 
Steatite,  250. 
Stratified  rocks, 
Stromboli,  93. 
Sulphur,  248. 

T. 

Tertiary,  224. 

Tides,  cutting  acHon,  122. 

life-feeding  action,  124. 
Tin,  247. 
Trap  dykes,  72. 
Triassic,  217. 
Turner's  Falls,  218. 

U. 

Underground  water,  74. 

V. 

Valleys,  13. 
Veins,  mineral,  66. 
Vertebrates,  179. 
Vesuvius,  92. 
Voice  of  animals,  187. 
Volcanoes,  88. 

dust  of,  36. 

cause  of,  90. 

W. 

Water,  expansion  in  freezing,  4. 

dissolving  action  of,  44,  62. 
heat-carrying  power  of,  64 
work  of,  62. 
underground,  74. 

Y. 

Yosemite  Valley,  121. 

Z 

Zinc,  246. 

blende,  246. 


This  book  is  DUE  on  the  last  date  stamped  below 


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